Colliding Neutron Stars can Generate Long Gamma-ray Bursts
by Evan Gough on December 7, 2022 at 11:46 pm
Gamma-Ray Bursts (GRBs) are the most energetic recurring events in the Universe. Only the Big Bang was more energetic, and it was a singularity. Astronomers see GRBs in distant Universes, and a lot of research has gone into understanding them and what causes them.
A new paper is upending some of what scientists thought they knew about these extraordinary explosions.
The discovery of GRBs dates back to the Cold War. As nuclear weapons testing proliferated through the 1950s and 60s, the US and the Soviet Union signed the Partial Test Ban Treaty. The treaty banned all nuclear weapons testing except for underground tests. Nuclear detonations release gamma rays and the US built and launched the Vela satellites to monitor the Soviet Union’s adherence to the treaty.
The Vela satellites started detecting bursts of gamma radiation, but scientists soon realized that they weren’t coming from nuclear weapons or even from Earth. Eventually, scientists at the Los Alamos Scientific Laboratory determined the sky positions for 16 GRBs. Researchers published a paper in the Astrophysical Journal in 1973 eliminating the Sun or the Earth as the sources for the GRBs, and the study of GRBs was born.
Now we know a lot more about these events. There are two categories of GRBs: short gamma-ray bursts and long gamma-ray bursts. (There’s a third sub-category called extremely long gamma-ray bursts.)
Scientists tell us that the light curves from GRBs are very complex, and no two are identical. But despite their lack of similarity, astrophysicists have determined their sources. The long ones come from stars that explode as supernovae and then form neutrons stars or black holes. The short ones come from kilonovae. Kilonovae are the result of either a pair of merging neutron stars or a neutron star merging with a black hole.
But a new study is throwing a wrench into our understanding.
The study is “A kilonova following a long-duration gamma-ray burst at 350 Mpc,” and it’s published in the journal Nature. The lead author is Jillian Rastinejad, a Ph.D. student in the Department of Physics & Astronomy at Northwestern University.
Astrophysicists have long believed that long gamma bursts are only caused by supernovae. They also believed that short GRBs come only from kilonovae. But the new study shows us something different. It shows that at least some neutron star mergers can produce long GRBs.
During a GRB, the gamma rays are observed first. But astrophysicists have to wait for the rest of the energy from the precursor event before they know if it was a supernova or a kilonova that caused it.
In December 2021, the team detected a 50-second-long GRB in a galaxy 1.1 billion light-years from Earth. Its name is GRB211211A (2021 is the year, 12 is the month, and 11 is the date of discovery). Two facilities detected it: the Swift Observatory’s Burst Alert Telescope and the Fermi Gamma-ray Space Telescope. A GRB of that length is a long gamma-ray burst, and according to established theory, it should’ve come from a supernova.
But GRBs from a supernova emit an extraordinarily luminous afterglow. The team looked at the region that spawned the GRB with telescopes that can observe all across the electromagnetic spectrum. They watched for the telltale afterglow indicating that a supernova caused the GRB, and there was none. The team was starting to understand that they were seeing something new.
“The weather was worsening in Hawaii, and we were so disappointed because we were starting to uncover hints that this burst was unlike anything we had seen before,” Rastinejad said. “Luckily, Northwestern provides us with remote access to the MMT Observatory in Arizona, and an ideal instrument was being put on that telescope the next day. It was cloudy there, but the telescope operators knew how important this burst was and found a gap between the clouds to take our images. It was stressful but so exciting to get those images in real-time.”
Instead of the tell-tale signs of a supernova, they observed evidence of a kilonova, showing that kilonovae can create long-duration GRBs. This goes against our established understanding.
“This event looks unlike anything else we have seen before from a long gamma-ray burst,” said lead author Jillian Rastinejad. “Its gamma rays resemble those of bursts produced by the collapse of massive stars. Given that all other confirmed neutron star mergers we have observed have been accompanied by bursts lasting less than two seconds, we had every reason to expect this 50-second GRB was created by the collapse of a massive star. This event represents an exciting paradigm shift for gamma-ray burst astronomy.”
The team expected to find evidence of a supernova, but they didn’t. Kilonovae fade quickly, whereas the brightness from supernovae persists for months. In this case, the object that caused the GRB was faint and quickly faded. The consequences of their unexpected findings became clear to them pretty quickly.
“When we followed this long gamma-ray burst, we expected it would lead to evidence of a massive star collapse,” said Northwestern’s Wen-fai Fong, a senior author on the study. “Instead, what we found was very different. When I entered the field 15 years ago, it was set in stone that long gamma-ray bursts come from massive star collapses. This unexpected finding not only represents a major shift in our understanding but also excitingly opens up a new window for discovery.”
Massive stars that explode as supernovae have many times more mass than our Sun, enough to power a longer afterglow. That material falls toward the black hole created by the supernovae but takes its time. The in-falling material is guided away from the black hole in jets, which we see as afterglow.
But neutron stars are small, and astrophysicists thought they simply don’t contain enough material to power a long afterglow, even when two of them merge. “When you put two neutron stars together, there’s not really much mass there,” Fong explained. “A little bit of mass accretes and then powers a very short-duration burst. In the case of massive star collapses, which traditionally power longer gamma-ray bursts, there is a longer feeding time.”
The afterglow that followed the GRB was also unusual in other ways. It contained high-energy gamma rays that started 1.5 hours post-burst and lasted more than 2 hours. Alessio Mei, a doctoral candidate at the Gran Sasso Science Institute in L’Aquila, Italy, led a group that studied the same data. Their paper was also published in Nature.
Mei and his team have an idea why the kilonovae created such a long afterglow. “This is the first time we’ve seen such an excess of high-energy gamma rays in the afterglow of a merger event. Normally that emission decreases over time,” said Mei. “It’s possible these high-energy gamma rays come from collisions between visible light from the kilonova and electrons in particle jets. The jets could be weakening ones from the original explosion or new ones powered by the resulting black hole or magnetar.” (A magnetar is a neutron star with extremely powerful magnetic fields.)
The study of GRBs is fascinating in its own right, and these findings are a new window into GRBs and the events that cause them. But there’s more to this than just the powerful burst. Kilonovae play an important role in creating the Universe’s heavy elements.
It took decades for scientists to understand how all the elements formed. In 2019, a paper in Nature put one of the last pieces of the puzzle into place. It showed that a kilonova explosion in 2017 contained the element strontium. Scientists knew that an atomic process called the r-process was responsible for about half of the atomic nuclei heavier than iron. The r-process is also called the rapid neutron capture process, and it allows an atomic nucleus to capture neutrons faster than it can decay. Scientists thought kilonovae were the site of the r-process, and the 2019 paper was the definitive proof.
Kilonovae are tough to study because they don’t last long. But this discovery of a kilonova with a long gamma-ray burst could help change that by giving scientists a way to spot more kilonovae.
“Kilonovae are powered by the radioactive decay of some of the heaviest elements in the universe,” Rastinejad said. “But kilonovae are very hard to observe and fade very quickly. Now, we know we can also use some long gamma-ray bursts to look for more kilonovae.”
To understand exactly what elements are present in a kilonova, scientists need to use spectroscopy. That’s difficult to do from the ground. There’s a new space telescope that specializes in exquisitely-detailed spectroscopy, but it, unfortunately, was not part of this work.
“With the JWST, we could have obtained a spectrum of the kilonova,” said Rastinejad. “Those spectral lines provide direct evidence that you have detected the heaviest elements.”
Observations by multiple telescopes are at the heart of this discovery. GRB detections by Swift and Fermi were only the beginning. This shows how important coordinated efforts involving many people and facilities are to making progress on complicated events like kilonova explosions. The image of a lone astronomer sitting at her telescope for long hours before finally shouting “Eureka!” is now apocryphal.
“This result underscores the importance of our missions working together and with others to provide multiwavelength follow-up of these kinds of phenomenon,” said Regina Caputo, Swift project scientist at NASA’s Goddard Space Flight Center. “Similar coordinated efforts have hinted that some supernovae might produce short bursts, but this event is the final nail in the coffin for the simple dichotomy we’ve used for years.”
“You never know when you might find something surprising,” Caputo said.
- Press Release: Surprise kilonova upends established understanding of long gamma-ray bursts
- New Research: A kilonova following a long-duration gamma-ray burst at 350 Mpc
- Press Release: NASA Missions Probe Game-Changing Cosmic Explosion
- New Research: Gigaelectronvolt emission from a compact binary merger
- Universe Today: The Expanding Debris Cloud From the Kilonova Tells the Story of What Happens When Neutron Stars Collide
The post Colliding Neutron Stars can Generate Long Gamma-ray Bursts appeared first on Universe Today.
“Early Dark Energy” Could Explain the Crisis in Cosmology
by Matt Williams on December 7, 2022 at 11:02 pm
In 1916, Einstein finished his Theory of General Relativity, which describes how gravitational forces alter the curvature of spacetime. Among other things, this theory predicted that the Universe is expanding, which was confirmed by the observations of Edwin Hubble in 1929. Since then, astronomers have looked farther into space (and hence, back in time) to measure how fast the Universe is expanding – aka. the Hubble Constant. These measurements have become increasingly accurate thanks to the discovery of the Cosmic Microwave Background (CMB) and observatories like the Hubble Space Telescope.
Astronomers have traditionally done this in two ways: directly measuring it locally (using variable stars and supernovae) and indirectly based on redshift measurements of the CMB and cosmological models. Unfortunately, these two methods have produced different values over the past decade. As a result, astronomers have been looking for a possible solution to this problem, known as the “Hubble Tension.” According to a new paper by a team of astrophysicists, the existence of “Early Dark Energy” may be the solution cosmologists have been looking for.
The study was conducted by Marc Kamionkowski, the William R. Kenan, a junior professor of physics and astronomy at Johns Hopkins University (JHU), and Adam G. Riess – an astrophysicist and Bloomberg Distinguished Professor at JHU and the Space Telescope Science Institute (STScI). Their paper, titled “The Hubble Tension and Early Dark Energy,” is being reviewed for publication in the Annual Review of Nuclear and Particle Science (ARNP). As they explain in their paper, there are two methods for measuring cosmic expansion.
The direct method involves using supernovae as “standard candles” (distance markers) to conduct measurements on the local scale. The indirect method involves comparing measurements of the CMB with cosmological models – like the Lambda Cold Dark Matter (LCMD) model, which includes the presence of Dark Matter and Dark Energy. Unfortunately, these two methods produce different results, the former yielding a value of ~73 km/s per megaparsec (Mpc) and the latter yielding ~67 km/s Mpc. As Dr. Reiss broke it down to Universe Today via email:
“The Hubble constant is the present rate at which the Universe expands. The Hubble tension is a discrepancy in the value you find for the Hubble constant when you either measure the expansion rate as best you can at present or you predict the value it should have based on the way the Universe looked after the Big Bang coupled with a model of how the Universe should evolve. Its a problem because if these two ways do not agree, it makes us think we are misunderstanding something about the Universe.”
But as Reiss adds, the mystery of the Hubble Tension is not as much of a problem as it is an opportunity for new discovery. So far, many candidates have been offered to explain the discrepancy, ranging from the existence of extra radiation, modified General Relativity (GR), Modified Newtonian Dynamics (MOND), primordial magnetic fields, or the existence of Dark Matter and Dark Energy during the early Universe that behaved in different ways. These can generally be divided into two categories: early-time (shortly after the Big Bang) and late-time solutions (more recently in cosmic history).
Late-time solutions postulate that the energy density in the post-recombination Universe – when the ionized plasma of the early Universe gave rise to neutral atoms (ca. 300 000 years after the Big Bang) – is smaller than in the standard LCMB model. Early-time solutions, meanwhile, postulate that the energy density was somehow increased before recombination occurred so that the “sound horizon” (the comoving distance a sound wave could travel) is decreased. For the sake of their study, Kamionkowski and Kenan considered Early Dark Energy (EDE) as a potential candidate.
As Reiss explained, the presence of EDE would have contributed about 10% of the total energy density of the Universe before recombination occurred. After recombination, the energy density would have decayed faster than other forms of radiation, thus leaving the late evolution of the Universe unchanged. “It would produce a burst of extra, unexpected expansion in the young Universe that, if we didn’t know about it, would cause the predicted value to underestimate the true value,” said Reiss.
What makes EDE preferable to late-time solutions is how the latter implies the existence of a fluid that effectively creates energy out of nothing – which violates the strong energy condition predicted by GR. What’s more, such models are difficult to reconcile with the Cosmic Distance Ladder measurements of Cepheid variables and Type Ia supernovae in nearby galaxies (low-redshift targets) and Type Ia supernovae in distant galaxies (high-redshift). In short, solutions that involve modifications to early-Universe dynamics appear to be most consistent with established cosmological constraints.
As they note, while there is a growing body of evidence that hints at the existence of EDE, our current measurements on the CMB are not precise and robust enough yet to distinguish EDE models from the standard LCDM model. What is needed, moving forward, are improved local measurements that will help refine the Hubble Constant and remove any systematic errors. Second, more precise measurements of CMB polarization on smaller angular scales are needed to test EDE and other new physics models.
As they indicate in their paper, these steps are already being taken thanks to observatories the Dark Energy Survey and next-generation observatories, like the James Webb Space Telescope (JWST) and the ESA’s Euclid mission:
“Fortunately, the next steps in exploring the Hubble tension are clear. Moreover, the required observational infrastructure is already in place, as it coincides largely with that assembled to study (late-Universe) dark energy and inflation. Ultimately, we must continue to explore astrophysical and measurement uncertainties. As we have learned over and over in cosmology, there is no single bullet – robust conclusions are only reached with multiple observational avenues and a tightly knit web of calibrations, cross-calibrations, and consistency checks.”
Further Reading: arXiv
The post “Early Dark Energy” Could Explain the Crisis in Cosmology appeared first on Universe Today.
How Artificial Intelligence Can Find the Source of Gamma-Ray Bursts
by Paul M. Sutter on December 7, 2022 at 10:20 pm
Gamma-ray bursts come in two main flavors, short and long. While astronomers believe that they understand what causes these two kinds of bursts, there is still significant overlap between them. A team of researchers have proposed a new way to classify gamma-ray bursts using the aid of machine learning algorithms. This new classification scheme will help astronomers better understand these enigmatic explosions.
Ever since the 1960’s, astronomers have identified brief intense bursts of high energy gamma ray radiation. These bursts come from all over the sky, and so they likely come from outside the galaxy. Over the decades astronomers have identified two different kinds of these gamma-ray bursts, which they call short and long. The short ones last for less than 2 seconds on average and account for around 30% of all bursts. The remainder, the long ones, tend to be much brighter than their shorter counterparts.
Most astronomers believe that different processes lead to the two different populations of gamma-ray bursts. It’s thought that mergers of compact objects like neutron stars lead to the short gamma-ray burst emissions. And on the other hand, it’s likely that exotic kinds of supernova explosions lead to the long ones. In the latter case, if large enough stars explode with high enough rotation rates, the exploding material can swirl around and form a beam of radiation that blasts out into space. If that beam happens to point towards the Earth, we see it as a long gamma-ray burst.
But telling the difference between the two is difficult. Many gamma-ray bursts sit right on the boundary between short and long, and some explosions share qualities of both.
A team of researchers have proposed a new mechanism for distinguishing these two classes of observations. They employed machine learning algorithms trained on existing data sets and computer simulations to find the key distinguishing features between short and long gamma-ray bursts. They found that they were able to cleanly separate the populations of observations even when the duration time of the blast was right at the boundary.
The astronomers hope that this tool will be useful to help easily classify future observations, which can then be used to refine our understanding of the physical mechanisms behind the explosions.
The post How Artificial Intelligence Can Find the Source of Gamma-Ray Bursts appeared first on Universe Today.
The Geminids Will be Peaking on December 14th. They’re Usually the Most Active Meteor Shower Every Year
by Andy Tomaswick on December 7, 2022 at 8:40 pm
Meteor showers are a great way to share a love of astronomy with those who might not be as familiar with it. Almost everyone loves watching streaks of light flash across the sky, but usually, it’s so intermittent that it can be frustrating to watch. That’s not the case for the next few weeks, though, as the annual Geminid meteor shower is underway until December 24th.
The Geminids are one of the most active meteor showers of the year. But, unlike many others, their source is an asteroid rather than a comet. 3200 Phaethon, named after the son of Helios, the Greek god of the Sun, is the named asteroid that travels closer to the Sun than any other. Part of that path crosses Earth’s orbit, and even though it is technically an asteroid, Phaethon acts somewhat like a comet when it gets close to the Sun, shedding particles that eventually end up burning up in Earth’s upper atmosphere as meteors.
This year, that light show will peak around the night of the 13/14th of December. Typically, astronomers can look toward the constellation Gemini and, in particular, the bright star Castor. It is an approximate sky location for the meteor shower’s “radiant,” meaning that most visible meteors will start somewhere near.
There are a few confounding factors for observers this year, however. The first is the Moon. It will be in a waning gibbous phase and will be approximately 72% full on the night of the 13th, making this year a much brighter night than average. Also, the Moon will rise at around 10 PM local time, so there will only be a few hours of actual darkness on the night of the 13th before the Moon’s light makes its presence known and washes out the light show for many smaller meteors.
Gemini will also be near the horizon in those few hours, making it challenging to see meteors that slope “downward” toward the horizon itself. However, many of the early meteors are unable to penetrate far into the atmosphere and therefore end up actually taking longer to burn up. Known as “Earthgrazers,” these meteors make up some of the more spectacular meteors in the shower.
As anyone in the northern hemisphere will tell you, the weather is another potential difficulty. December isn’t known for its clear nights, which might be no exception on the 13th. However, the Geminids will still be visible on other nights, though there is a dropoff of about 50% each night, and exponential decays like that mean that very quickly, there will hardly be any at all. At its peak and without any moonlight, amateur astronomers could see anywhere up to 1 meteor per minute on the night of the 13th.
If the clouds roll in on the 13th in your area, you can at least take some solace in the fact that the Moon will rise 30 minutes later the next night and 30 minutes later again the night after that, providing more time for some unobstructed viewing. And if you decide to take the time to do so, organizations such as the American Meteor Society could use your help in cataloging this year’s Geminid shower. There’s a link below to an article they wrote on the shower and a guide on how and where to provide any quantitative data that you might be interested in taking during your meteor-watching expedition. Now the best everyone can do is hope for clear skies in the not-too-distant future.
Time lapse of the Geminid meteor shower in Arizona and an inset of a time-lapse in France.
Credit – Malcolm Park & Michel Deconinck
A Star was Blocking a Galaxy, but Now it’s Moved Enough That Astronomers can Finally Examine What it Was Hiding
by Evan Gough on December 7, 2022 at 6:45 pm
One of the biggest puzzles in astronomy, and one of the hardest ones to solve, concerns the formation and evolution of galaxies. What did the first ones look like? How have they grown so massive?
A tiny galaxy only 20 million light-years away might be a piece of the puzzle.
One critical difference between the Universe shortly after the Big Bang and the Universe we find ourselves in today is the different metallicity. The early Universe was almost completely made of the two lightest elements, hydrogen and helium. So the stars in the earliest galaxies contained hydrogen and helium. Only as generations of stars lived and died was the Universe populated with heavier elements—things like carbon, oxygen, and iron—which astronomers call metals. Stars forge these metals via nucleosynthesis and then spread them out into the Universe when they die, to be taken up in the following generations of star formation. The heavier elements are critical in the formation of planets like Earth and lifeforms like us.
So a young galaxy with very low metallicity is an oddball, and observing it can be like looking back in time.
The tiny galaxy is called HIPASS J1131–31. But its nickname, Peekaboo, is more descriptive. That’s because, in the last 50 to 100 years, a fast-moving foreground star that was blocking Peekaboo from view has moved aside, letting the Hubble and other telescopes get a better look at it.
“Uncovering the Peekaboo Galaxy is like discovering a direct window into the past, allowing us to study its extreme environment and stars at a level of detail that is inaccessible in the distant, early universe,” said astronomer Gagandeep (Deep) Anand of the Space Telescope Science Institute, and co-author of the new study on Peekaboo’s intriguing properties.
Now that the intervening star has moved out of the way, astronomers have studied the tiny galaxy’s metallicity and other properties. The results of those observations are in a new paper in the journal Monthly Notices of the Royal Astronomy Society titled “Peekaboo: the extremely metal-poor dwarf galaxy HIPASS J1131–31.” The lead author is I D Karachentsev from the Special Astrophysical Observatory of the Russian Academy of Sciences, Nizhnij Arkhyz, Karachay-Cherkessia.
As a dwarf galaxy, it contains far fewer stars than massive galaxies like our Milky Way. Remarkably, though Peekaboo is 20 million light-years away, the Hubble Space Telescope was able to resolve about 60 of its individual stars. Observations with the Hubble and other facilities like the South African Large Telescope (SALT) showed that its stellar population is only a few billion years old. Stars this young should have higher metallicity than they do because so many stars lived and died before they formed.
Professor Bärbel Koribalski, an astronomer at Australia’s national science agency CSIRO, first detected Peekaboo 20 years ago and is a co-author of the new paper.
“At first, we did not realize how special this little galaxy is,” Koribalski said of Peekaboo. “Now, with combined data from the Hubble Space Telescope, the Southern African Large Telescope (SALT), and others, we know that the Peekaboo Galaxy is one of the most metal-poor galaxies ever detected.”
Galaxies in the local universe typically contain a good proportion of ancient stars that are billions of years old. These are called Red Giant Branch (RGB) stars, and they’re so old they’ve left the main sequence, stopped fusing hydrogen into helium, swelled in volume and cooled. Because they’re cooler, they appear red.
But Peekaboo lacks a similar population of older red stars. Instead, Peekaboo is a compact blue dwarf galaxy, and the colour blue signifies a high proportion of hot young stars. It contains some RGB stars, but not as many as expected. “In each case, the RGB is very insubstantial compared with the evident young populations,” the authors write, describing Peekaboo and a few similar galaxies that we know of. Since these hot blue stars are so young, they should have a higher metallicity.
Peekaboo is extraordinarily interesting, but it’s not completely unique. “The compact dwarf galaxy Peekaboo with a predominantly young stellar population and very low metallicity is not unique in the Local Volume,” they write in their paper.
Peekaboo is an example of an extremely metal-poor (XMP) galaxy. What sets it apart from other XMP galaxies in the local Universe, like I Zwicky 18, is its proximity to Earth. It’s only about 20 million light-years away—almost next door in astronomical terms—while the other XMP galaxies we know of are twice that distance away.
Peekaboo’s stellar population makes it one of the youngest and lowest-metallicity galaxies in the local universe. 13 billion years have passed in the local universe, and Peekaboo should have developed a higher metallicity than it has. (The term ‘Local Universe’ describes a region in space centred on an observer with a radius of R < 300 Mpc (z < 0.1) containing large-scale structures like groups, voids, clusters, and superclusters. It’s a large enough scale that the Universe appears both homogeneous and isotropic.)
What Peekaboo can tell us about the evolution of galaxies will have to wait. This study is based on observations from a survey called the “Every Known Nearby Galaxy Survey,” and Hubble’s job was to gather as much data on as many neighbouring galaxies as it could. The next step is to focus on Peekaboo with the Hubble and the JWST to study the tiny galaxy’s stars and metallicity in greater detail. That’s why its proximity to us is so important.
“Due to Peekaboo’s proximity to us, we can conduct detailed observations, opening up possibilities of seeing an environment resembling the early universe in unprecedented detail,” Anand said.
For now, there’s uncertainty around Peekaboo. “The situation with Peekaboo is decidedly ambiguous,” the authors write in their conclusion. How can it have such low metallicity when 13 billion years have passed in the Local Universe?
As for the puzzle about how galaxies form and evolve, Peekaboo could end up being an important piece. We’ll have to wait for the team’s follow-up observations to find out.
- Press Release: Peekaboo! Tiny, Hidden Galaxy Provides a Peek Into the Past
- Published Research: Peekaboo: the extremely metal-poor dwarf galaxy HIPASS J1131-31
- Universe Today: Astronomers Find the Hollowed-Out Shell of a Dwarf Galaxy that Collided With the Milky Way Billions of Years Ago
Will We Ever Go Back to Explore the Ice Giants? Yes, If We Keep the Missions Simple and Affordable
by Evan Gough on December 6, 2022 at 11:02 pm
It’s been over 35 years since a spacecraft visited Uranus and Neptune. That was Voyager 2, and it only did flybys. Will we ever go back? There are discoveries waiting to be made on these fascinating ice giants and their moons.
But complex missions to Mars and the Moon are eating up budgets and shoving other endeavours aside.
A new paper shows how we can send spacecraft to Uranus and Neptune cheaply and quickly without cutting into Martian and Lunar missions.
The demands of deeper, scientifically fulfilling missions to Mars and the Moon are squeezing the budgets of NASA, the ESA, and other agencies. But there are fascinating worlds further out in the Solar System that are begging to be explored. Especially the ice giants Uranus and Neptune.
NASA has a strong focus on Mars and the Moon right now. The eventual Mars Sample Return mission will be resource intensive, as will the Artemis program. But the ice giants demand attention, too, even though we can never land there or gather samples from them. They played a role in the evolution of the Solar System, they’re similar to many exoplanets we find in distant solar systems, and our brief encounters with them gave us only tantalizing glimpses.
The last spacecraft to fly past Uranus was Voyager 2 in 1986, and it was the only one. It got to within 81,500 kilometres (50,600 miles) of the planet’s cloud tops. Voyager 2 was also the last and only spacecraft to fly past Neptune, coming to within 4,800 kilometres (2,983 miles) above the planet’s north pole in 1989. Imagine what dedicated orbiters could discover with modern technology.
The Hubble space telescope has tried to fill in the gaps in our understanding of the Solar System’s pair of ice giants. But it struggles to reveal details from a distance. The James Webb Space Telescope has shown its ability to study our Solar System’s planets with its fascinating images of Jupiter, but it has other jobs to do. Observations from a distance will always have their limitations and can never replace purpose-built missions.
Philip Horzempa, from LeMoyne College at Syracuse University, says that we can explore both Uranus and Neptune if we’re guided by two simple words: simple and affordable. In a white paper submitted to the National Academies of Sciences, Horzempa outlines the case for building a pair of orbiters to visit Uranus and Neptune. He explains how they needn’t be ground-breaking designs, and they needn’t be flagship missions.
Instead, NASA could rapidly develop missions to both ice giants that could gather important scientific data without breaking their budget. Launch windows are approaching for missions to both planets, and rather than propose elaborate missions that may never get approved, NASA should develop reasonable missions that can advance our understanding of both worlds.
Horzempa points out that there’s a historical precedent for this. Some of NASA’s best missions were only launched as more streamlined, cheaper versions of their original proposals. The Viking Mars landers were eventually launched as more streamlined versions of an initial mission proposal. NASA’s Grand Tour program in the 1970s called for four probes: two would’ve visited Jupiter, Saturn, and Pluto. Two more would’ve visited Jupiter, Uranus, and Neptune. But the program was enormously expensive and was cancelled. Instead, NASA launched Voyager 1 and 2. The New Horizons mission and the Parker Solar Probe have similar backstories.
Timing is critical. Later this decade, there are two launch windows that can take advantage of Jupiter gravity-assist maneuvers. “In order to take advantage of the first Jupiter assist, it is imperative that Phase A should begin for a Neptune Orbiter in 2022,” Horzempa writes, so time is running out. “This abbreviated timeline dictates the use of a simple craft with no atmosphere Probe.”
Ideal missions to both planets would include orbiters and atmospheric probes. Both planets likely have solid cores, but the rest of their compositions are very strange and might include regions where methane decomposes into diamond crystals that rain downward like hailstones into oceans of liquid carbon. We’ve got a lot to learn about Uranus and Neptune and their atmospheres, but more detailed studies with probes will have to wait.
Sacrificing an atmosphere probe is a trade-off worth making if it means that a mission can be launched to take advantage of gravity-assist maneuvers, according to Horzempa. “Key to affordability is the separation of the Probe missions from the Orbiters,” he writes. This makes the orbiters more simple and cheap, which increases the likelihood that they will be approved.
Probes could still come later, Horzempa says, which can be an advantage for future atmospheric probe missions to both ice giants. “The Orbiters <will> be given 1st priority in the launch queue. Since the Probe program will be untethered from the Orbiter effort, its mission cadence will be determined by factors unique to the study of giant planet atmospheres.”
All spacecraft are high-tech endeavours, but orbiters themselves are the most well-understood design. Rovers are enormously complex, and sample-return missions ratchet the complexity up even further, though neither of those is explicitly relevant to the ice giants. Restricting ice giant missions to orbiters only makes the missions feasible. “The Ice Giant Orbiters will build on the experience of previous such missions. By now, industry has ‘figured out’ how to construct such craft,” writes Horzempa.
For NASA, the 2020s is a decade of stiff competition for resources. Their budget will be stretched thin by Artemis, Mars Sample Return, and other programs like the Lunar Discovery program. But since missions to the ice giants can take so long, we run the risk of getting no new data from either planet for up to 40 years unless NASA acts now. “A radically new approach is called for if we are to obtain any new data in the coming 20-40 years,” Horzempa says.
One of the critical pieces for simple and affordable missions concerns the power source. Solar power is in short supply in the ice giants’ neighbourhood. Spacecraft travelling that far are designed around radioisotope thermoelectric generators. They contain radioactive isotopes that decay and release heat, which is then converted into electricity. This is the type of system that the New Horizons mission to Pluto uses.
Unfortunately, the development of the next generation of RTGs was cancelled. It was called the enhanced-MMRTG and would’ve delivered more power than previous RTGs. NASA has plans for a Next Generation RTG, but there are no firm dates attached to it and no guarantees it will be built.
This means that the standard MMRTG (Multi-Mission Radioisotope Thermal Generator) and solar power are the only available options. The orbiter missions are still doable, according to Horzempa. “This limitation means that the Ice Giant craft will need to be very frugal with their power demands.” It also means that the Uranus orbiter could be forced to get by on solar power because RTGs take time to build and may be needed for other applications. (MSL Curiosity and the Perseverance rover both use MMRTGs.) For distant Neptune, an RTG is the only option.
“Two fast, simple, affordable (FSA) orbiters can be launched if one of those crafts is solar-powered,” Horzempa explains. “Physics dictates that the single MMRTG be used for the Neptune Orbiter.”
Thanks to continued technological progress, solar power is now a feasible power source for a Uranus orbiter, as long as power consumption is managed rigorously. New designs are 20% lighter and one-quarter the volume of previous panels while delivering the same power output. “The ROSA (Roll-Out Solar Array) and Mega-ROSA panels can provide 200-400 W at 20 A.U.,” writes Horzempa. “The first ROSA array was launched to the ISS in 2017 and demonstrated its capability.”
With less power available, decisions will need to be made about science payloads. The words simple and affordable are still the guiding ideas, and Horzempa outlines how science payloads can adapt. The obvious first step is to limit the number of science devices.
As a flagship mission, the Juno mission to Jupiter holds nine scientific instruments. One of them, the JunoCam, was included solely to provide optical light images for the rest of us to enjoy and isn’t truly a science instrument. Simple and affordable orbiters to the ice giants won’t have the same payload capabilities as Juno.
But, perhaps ironically, a high-resolution camera is probably the primary instrument for missions to Uranus and Neptune.
“With a limited payload, first priority goes to imaging,” Horzempa writes. “The satellites of Uranus and Neptune are in dire need of complete, detailed photographic coverage.” Horzempa points out that creating charts is the first step in exploration, “… a tradition that is thousands of years old,” he explains.
“High-resolution and context cameras will produce those base maps,” he says, and by adding near-IR imagers, the orbiters can probe the atmospheres and the ring systems.
Decoupling probe missions from orbiter missions is one way to develop missions that are fast and affordable. But probe missions are too important to ignore completely.
Horzempa explains that while orbiter technology is well-established and can be employed more readily, probe technology has fallen behind. Proposals for a Saturn probe have been rejected, leaving that technology to languish. Before we can ever send atmospheric probes to the ice giants, we should send one to Saturn.
“The initial mission would be a Saturn Probe. That would satisfy a long-standing objective and develop the technology required for almost-identical Probes for Uranus and Neptune,” he writes. He also says that the Decadal Survey should “…advocate for combined KBO-Ice Giant Probe missions.”
In his white paper, Horzempa keeps coming back to the idea that flagship missions that try to accomplish too much at once are likely to be rejected. While flagship missions including probes are not the priority in ice giant missions, neither should probes be forgotten. The idea for orbiter-only missions to Uranus and Neptune makes more sense if there are also plans for future atmospheric probes.
“Flagship missions are wonderful, but they are useless if they are so complex that they never
get funded and never fly,” he writes. He refers to this as the ‘complexity trap.’ “Less ambitious missions will deliver less science, but they have a better chance of achieving a coveted New Start.”
NASA is considering a concept for a mission to Uranus and its moons. It’s called the Uranus Orbiter and Probe, and it’s a flagship mission that could be launched in 2031. It was being considered alongside a similar mission to Neptune called Neptune Odyssey. A flagship mission to Uranus makes logical sense because it follows similar missions to Jupiter and Saturn (Juno and Cassini.) But its potential expense means it may not be approved or developed in time. Horzempa’s argument is that we can visit both ice giants cheaply and rapidly if we trim down the missions.
Ultimately, it’s up to the Decadal Survey team to find the right mix. “This paper does not put forward a specific design but, rather, asks the Decadal team to endorse a competitive approach to the exploration of the Ice Giant systems,” Horzempa states in his conclusion. He says that NASA should set the cost, outline the objectives, and let the commercial sector tackle it. That will engender healthy competition.
There is never a shortage of worthwhile missions. Successful missions to destinations throughout the Solar System have only made us hungry for more. It’s been over 35 years since Voyager 2 performed its brief flybys of the ice giants. That spacecraft’s cameras were essentially TV cameras from the 1970s. Think of how much technology has advanced since then and how much we can learn from modern orbiters.
Horzempa makes a strong case for fast, simple, affordable missions that can take advantage of rapidly-approaching launch windows. Should NASA seize the opportunity?
- White Paper: Ice Giant Exploration Philosophy: Simple, Affordable
- NASA/JPL: Images Voyager Took of Neptune
- White Paper: Gas Giant and Ice Giant Atmospheres: Focused Questions for 2023-2032
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A new Hubble Image Reveals a Shredded Star in a Nearby Galaxy
by Seth Lockman on December 6, 2022 at 10:53 pm
The Hubble Space Telescope, to which we owe our current estimates for the age of the universe and the first detection of organic matter on an exoplanet, is very much doing science and still alive. It’s latest masterpiece remixes an old hit – apparently a growing trend in space science as well as space music.
Big Bada Boom
The story of this image begins roughly 165,000 years ago, when an unnamed O-type star in the Large Magellanic Cloud died in a type II supernova. Light from the explosion shot out in all directions, and about 160,000 years later a tiny cross section of that expanding sphere of light reached Earth. If humanity had modern telescopes around 3,000 BC, automated systems might have logged a blip in the southern constellation Dorado, well under the limits of human perception from such a great distance.
The supernova remnant took on a familiar form: a beautiful glowing cloud of expanding gas surrounding a pulsar – a super-dense and rapidly spinning neutron star with a powerful magnetic field. Shockwaves from the collapsing stellar core interacted with the nebula, coalescing the diffuse gas into filaments. Two especially hot and dense regions of gas shot away from the central pulsar in opposite directions, “bullets” likely fired off by the core’s powerful magnetic field. Within 5,000 years the nebula would be 75 light-years across, its heart still glowing at a million degrees.
People Are Noticing
The remnant was catalogued by Karl Henize in 1956 as part of a survey of emission nebulae in the Magellanic Clouds. Dubbed N49 (sometimes LMC N49) it was immediately recognized as a powerful radio emitter, and to this day it is the brightest supernova remnant in the Large Magellanic Cloud. On March 5, 1979 a historically powerful gamma ray burst was detected by all nine spacecraft of the interplanetary gamma-ray burst network. The source was quickly pinpointed as N49, which at this point was a usual suspect for this sort of mischief.
But The March 5 transient was so insanely powerful that a second otherwise-invisible neutron star in that region was hypothesized. The term “pulsar” wasn’t going to cut it for N49. This and other similar events spurred on the study of “soft gamma ray repeaters,” and eventually the creation of the “magnetar” classification in 1992.
The Hubble Space Telescoped first imaged N49 over 3 hours between November of 1998 and July of 2000. Three false-color images in the classic “Hubble Palette” – red for sulfur, blue for oxygen, and green for hydrogen – were captured using its Wide Field Planetary Camera 2 (WFPC2) and superimposed on a black-and-white base image, also captured by Hubble. The composited image was used in studies mainly focused on better understanding the nebula’s structure and environment.
N49 has at least 26 other identifiers across different catalogues. The most common byname in the press is DEM L 190. The remnant has been imaged by notables like ROSAT, Chandra, and Spitzer, and was even mentioned in Chapter 9 of the companion book to Carl Sagan’s Cosmos.
The remnant’s intrigue comes not just from its brightness and powerful EM bursts, but also its asymmetry. Think of the stunning Ring Nebula, the Cat’s Eye, or the Lion Nebula. Each of these monuments to the awesome beauty of the cosmos was created by the same basic process as N49. An observer of most planetary nebulae could be forgiven for entertaining the thought of a cosmic watchmaker.
By comparison N49 looks like that watchmaker tried to flip an omelet and really messed up. Pinning down why and how the occasional stellar remnant gets so messy will help us understand stellar life cycles more completely.
As imaging technology improves, from time to time the ESA/Hubble team revisits targets. For example, back in 2003 data from two UV filters centered at 300nm & 380nm were captured at the same time as the others but were not included in the original composite. For the 2022 image they were added in, and luminosity was depicted using red light instead of white, in part to give background stars a more natural-looking color.
The past nineteen years have also seen great strides in noise reduction and data stretching algorithms, which when applied to the updated image reveal an unprecedented level of detail. Fun fact, technically none of this improves the image’s resolution, which is limited by WFPC2’s performance back in the day. But that’s just a technicality – there’s no arguing the new 2022 image shows significantly more detail.
What will this new photo reveal to discerning eyes? That’s the fun part. Maybe the more detailed filaments will help astronomers better model especially violent stellar deaths. In a few years this photo may help answer questions we don’t even have yet.
For More Information:
- ESA’s page on Revisiting a celestial fireworks display
- NASA | ESA Hubble’s page on Revisiting a Celestial Fireworks Display (Colours & filters on the bottom-right of the page)
- Up your work chat game with NASA | ESA Hubble on Giphy
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Evidence of a Megatsunami on Mars
by Carolyn Collins Petersen on December 6, 2022 at 9:57 pm
Things were pretty wet back on Mars about three and a half billion years ago. You wouldn’t know that by looking at the planet today. But, would you believe a megatsunami happened there? It turns out that not one, but two of these rogue waves happened there some 3.4 billion years ago.
They occurred on the very spot where the Viking Lander settled down in 1976. Today, scientists know about these catastrophic floods, thanks to a re-examination of images of rock-strewn Chryse Planitia that Viking sent back.
Planetary Science Institute scientist Alexis Rodriguez studied the region in detail to figure out what happened to the region. It turns out that Viking’s landing spot contains deposits of material left by a pair of catastrophic floods. The second of these swept across the Martian landscape right after a three-kilometer-wide asteroid smacked into a Martian ocean. The fact that water once existed where Chryse Planitia is today isn’t a surprise. After all, that’s why Viking went there. But, figuring out how such a flood happened took a little detective work.
From orbital images available at the time, the Viking scientists selected the landing site because it looked like water once flowed there. “The lander was designed to seek evidence of extant life on the Martian surface, so to select a suitable landing site, the engineers and scientists at the time faced the arduous task of using some of the planet’s earliest acquired images, accompanied by Earth-based radar probing of the planet’s surface,” said Rodriguez, lead author of Evidence of an oceanic impact and megatsunami sedimentation in Chryse Planitia, Mars in Nature Scientific Reports. “In addition to meeting tight engineering constraints on the spacecraft’s orbital and descent paths, the landing site selection needed to fulfill a critical requirement—the presence of extensive evidence of former surface water.”
What Happened to Create a Megatsunami on Mars?
At first glance, Chryse Planitia looks dry, dusty, and rocky. But, it has all the hallmarks of rapidly flowing water. When water rushes across a landscape, it carries along rocks, sand, silt, and whatever else gets in the way. The same thing happened on Mars. Viking actually touched down on the lower edge of a flow feature called a fluvial channel. Chryse Planitia itself is a roughly circular plain north of the Martian equator. However, once Viking got on the ground, scientists noticed how boulder-strewn the region is. They decided that the area was a thick deposit either from multiple impacts or fractured lavas. The whole thing remained a mystery until Rodriguez started looking at the images and data again. His idea invokes more than one episode of catastrophic flooding.
In an earlier paper, he suggested that 3.4 billion years ago, there were two Martian megatsunamis. They smacked into the ancient ocean, sending huge waves across the Martian landscape. Between them, the ocean receded quite a bit and the climate became much colder. Rodriguez also identified a possible marine impact crater—Pohl crater—which likely generated the second of these two megatsunamis.
“Pohl is outstanding in several respects; it is atop immense fluvial landscapes formed by ocean-generating floods, and it is partly covered by the second megatsunami. Hence, we know that it must have formed after the ocean’s generation and before its disappearance,” said Anthony Lopez, a geosciences undergraduate student at Pima Community College and an intern working with Rodriguez.
A Map View of the Mars Megatsunami
Simulating and Mapping the Catastrophe
To get a better idea of what happened, Rodriguez and his team used a variety of mosaic images from Mars Reconnaissance Orbiter, Mars Odyssey, Mars Orbiter, and Mars Global Surveyor missions to produce detailed maps of the region. They mapped the distribution of water-related features within Chryse Planitia. Then, they searched for a relevant impact site—which turned out to be Pohl Crater. It wasn’t the first impact to smack into the region, but it created the fluvial plain the Viking lander studied. That second impact landed in the ocean. At that point, the ocean waters flowed catastrophically over the region. The flooding obliterated previous flow channels and created the deposits that Viking 1 landed on billions of years later.
The team also simulated the impact to understand the extent of its influence. “The simulated run-up extents of Pohl’s impact-generated megatsunami accurately reproduce the previously mapped margins of the older megatsunami, providing further robust support to the megatsunami – and hence ocean – hypothesis and this crater’s interpretation as its source,” said co-author Darrel Robertson of NASA’s Ames Research Center.
“The simulation clearly shows that the megatsunami was enormous, with an initial height of approximately 250 meters, and highly turbulent. Furthermore, our modeling also shows some radically different behavior of the megatsunami to what we are accustomed to imagining. Notably, the seismic shaking associated with the impact would have been so intense that it could have dislodged sea floor materials into the megatsunami, densifying some wave fronts into run-up debris flows.”
It appears that the megatsunami reached the Viking 1 lander site and could well have affected Pathfinder’s landing site, about 850 kilometers away. Ultimately, it may have helped create a new inland sea in the region.
Implications for Ancient Life?
While this study doesn’t prove anything about life on ancient Mars, it certainly reveals environments where it could have existed. “The ocean is thought to have been groundwater-fed from aquifers that likely formed much earlier in Martian history—over 3.7 billion years ago—when the planet was “Earth-like” with rivers, lakes, seas, and a primordial ocean,” said Rodriguez. “Consequently, the ocean’s habitability could have been inherited from that Earth-like Mars; the development of transient habitability is not sufficient; we need sustained continuity. So, the Viking 1 lander site was well suited to carry out the life detection experiment.”
With Viking and Pathfinder both in Chryse Planitia, it could well be that NASA’s probes have already sampled a couple of diverse marine environments on Mars. The next steps now are to see if Pohl could be a good landing site for further studies. Could it have been habitable? What will the geologic record tell us about the ancient ocean’s chemistry? Rodriguez says the science merits a second look, now that we know what happened there.
“Right after its formation, the crater would have generated submarine hydrothermal systems lasting tens of thousands of years, providing energy and nutrient-rich environments. As for specific targets, we find numerous possible mud volcanoes over areas of the second megatsunami covering and surrounding Pohl. Our observations suggest that these features extruded regionally megatsunami-retained seawater and marine sediments during extended geologic times. Sampling these materials would maximize the odds of directly probing the habitability of this Mars early ocean,” he said. “Our future characterizations will seek to identify a relatively small site offering access to the entire marine record. Such a terrain would merit a rover’s visit.”
For More Information
Not Just Stars. Gaia Mapped a Diverse and Shifting Universe of Variable Objects
by Andy Tomaswick on December 6, 2022 at 6:57 pm
We’ve reported on Gaia’s incredible data-collection abilities in the past. Recently, it released DR3, its latest data set, with over 1.8 billion objects in it. That’s a lot of data to sift through, and one of the most effective ways to do so is through machine learning. A group of researchers did just that by using a supervised learning algorithm to classify a particular type of object found in the data set. The result is one of the world’s most comprehensive catalogs of the type of astronomical object known as variables.
By definition, variables change their brightness over time. And Gaia, which has been monitoring vast parts of the sky for long periods, is particularly adept at finding them. In fact, it found something on the order of 12.4 million variable sources, about 9 million of which were stars. The over 3 million or so were either active galactic nuclei or galaxies themselves. All of these objects had changes in their brightness at some point or another throughout Gaia’s observation of them.
Admittedly, 12.4 million out of 1.8 billion is only about .6% of the total observed objects in DR3. However, that is still a lot of data to work with, and they might hold information that astronomers would like to understand about what causes certain types of variability.
According to the researchers, those causes result in very different kinds of variability – 25 different kinds to be precise. Their paper, released on arXiv, includes categories such as pulsating, eclipsing, rotating, microlensing, and cataclysmic. That last one sounds exciting, and there are 7306 of them in the data set, though the brightness of these events varied widely even within individual categories.
To sort the 12.4 million objects into each of these categories, the researchers turned to one of the most useful algorithms to do just that – machine learning. In particular, they used a technique called “supervised classification.” Basically, that means they had a human help an AI algorithm identify features of a certain classification and then provided manual feedback on whether an object met the criteria for classification into that category.
Eventually, the algorithms could pick up on defining features of the different categories and sort objects that humans had never looked at into those categories relatively accurately. The specific features that define each category are also defined in the paper. For example, the cataclysmic variables have a higher level of variability probability than other objects in the data set.
Plenty of manual data massaging went into the final collection, though it was also discussed at length in the 105-page paper. However, there were some fundamental issues with how Gaia observes objects that could eliminate some potential variables from this collection. For example, Gaia doesn’t sample the whole sky all the time, so variables whose variability lasts less than a set amount of time might be missed if Gaia doesn’t happen to peer their way during the changes. This isn’t likely to be a large number of variables, but some are undoubtedly missed in this data set.
What the data set does represent, though, is the world’s most comprehensive catalog of variable astronomical objects and the tools to do science to them. These sorts of data releases are precisely the kind of milestones that keeps astronomy moving forward. And Gaia still has more to come, with DR4 on the way sometime after 2025. So astronomers will have plenty of time to pour over all the DR3 data in detail before the next massive data release.
Rimoldini et al – All-sky classification of 12.4 million variable sources into 25 classes
UT – Gaia is an Even More Powerful Planet Hunter Than we Thought
UT – ESA is About to Release its Third Giant Data Release From Gaia
UT – Gaia’s Massive Third Data Release is out!
Artist’s depiction of Gaia in the Milky Way.
Credit – ESA / ATG medialab, background image: ESO / S. Brunier
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Mars at Opposition 2022: The Full Moon Occults Mars Wednesday Night
by David Dickinson on December 6, 2022 at 5:05 pm
A rare event transpires Wednesday night, as the Full Moon occults Mars near opposition.
Have you checked out Mars lately? The Red Planet currently rides high to the east at dusk, rising as the Sun sets. We call this opposition season, the biannual span when Mars passes closest to the Earth and offers observers optimal views of the planet. Mars opposition 2022 is special however, as three events converge in one night: Mars at opposition, the Moon reaches Full, and the Moon occults (passes in front of) Mars, all on the evening/morning of Wednesday/Thursday, December 7th/8th.
Celestial Dates with Destiny
You can see how the action around Mars stacks up in the first week of December:
1st- Mars passes nearest Earth (2:00 Universal Time/UT)
8th-Full Moon (4:00 UT)
8th-Mars Lunar Occultation (4:00 UT)
8th-Mars at Opposition (5:00 UT)
Note that Mars is closest to the Earth a week prior to opposition. This occurs for two reasons: while the Earth is moving towards perihelion in January (that is, we’re moving towards the Sun in December, but away from Mars), the Red Planet is doing the opposite, headed towards aphelion on May 30, 2023, just under six months after this week’s opposition. This makes up for the 900,000-odd kilometer difference as Mars is 0.55 Astronomical Units (AU, or 81.5 million kilometers) from Earth on the 1st, but sits 82.4 million kilometers from Earth at opposition.
In fact, we’re currently trending towards a cycle of unfavorable oppositions for Mars now, which will bottom out in February 2027 when Mars only reaches an apparent diameter of 13.8” as seen from the Earth. After 2027, Mars oppositions will slowly start to become more favorable again.
No Missions to Mars
Unfortunately, this Mars launch window also marks a sad milestone: for the first time since 2009, no mission will catch the biannual pre-opposition window to head to Mars. The European Space Agency’s ExoMars Rosalind Franklin rover was set to make the trip until Russia invaded Ukraine early this year, forcing ESA to look for another launch carrier and lander. ESA still hopes to get the rover to Mars by 2030.
‘Standing in the Shadow’ as the Moon occults Mars
But it’s Wednesday night’s occultation of Mars by the Full Moon that makes the 2022 opposition special. Opposition and the occultation plus the Full Moon all occur within an hour of each other. This is pretty rare: the near-Full Moon hasn’t occulted a naked eye planet or bright star since July 2019 (Saturn) and won’t do so again until May 24, 2024 (Antares), This is also the last of two occultations of Mars by the Moon for 2022, The Moon will occult Mars five times in 2023, though none are as favorable as the December’s event. The December ‘Long Night’s Moon’ nearest to the southward equinox also rides high in the sky for northern hemisphere observers, another plus.
This is also the closest Mars opposition versus a Full Moon with a lunar occultation for the 21st century. 21st century occultations of Mars near (less than 24 hours) from Full Moon also occur on December 24, 2007, January 14, 2025, February 5, 2042, May 28, 2048, February 27, 2059, and finally on April 27th 2078, which also features a shallow penumbral lunar eclipse.
The lunar occultation ‘footprint’ for Wednesday night’s occultation spans most of North America and Europe, with only the southeast U.S. missing out. Mars is 17” across during the event, shining at magnitude -1.9. The Moon will take just over half a minute to cover Mars during the occultation.
When to Watch
Here’s a table for select North American and European cities in the path of the occultation, with ingress/egress times. You can see an extensive list of sites and times here.
City Ingress Egress Detroit 3:20UT/10:20PM EST 4:09UT/11:09PM EST Dallas 2:54UT/8:54PM CST 3:28UT/9:28PM CST Los Angeles 2:30UT/6:30PM PST 3:30UT/7:30PM PST Seattle 2:51UT/6:51PM PST 3:50UT/7:50PM PST London 5:00UT/5:00AM BST 6:00UT/6:00 AM BST Helsinki 4:55UT/6:55AM EET 5:39UT/7:39 AM EET Table credit: Dave Dickinson.
Mars will be bright enough to follow riiiiiight up to the limb of the Full Moon during the event. The occultation occurs in the early morning hours for Europe on Thursday December 8th, and late in the evening of December 7th for North America. The disappearance of Mars behind the Moon will be visible even to the unaided eye, though binoculars or a small telescope will definitely help you enjoy the view.
Looking back from Mars, you’d be treated to an even stranger view, as the Moon transits the slim crescent Earth, just scant degrees from the Sun.
The Moon occults Mars: Weather Prospects, Watching Live
As of writing this, weather prospects for the contiguous United States (CONUS) look to favor the central northern states and the U.S. southwest.
Clouded out or simply live outside of the occultation footprint? Astronomer Gianluca Masi has you covered, with a live webcast as the Moon occults Mars, starting at 4:00 UT/11:00 PM EST Wednesday night.
The Moon Occults Mars: Spotting a ‘Daytime’ Red Planet
Finally… ever seen Mars in the daytime? It’s certainly possible near opposition… and the nearby Full Moon offers an excellent guide to complete this unusual feat of visual athletics. In North America, I’d start looking for Mars near the Moon just before local sunset, while in Europe, your best bet is to follow Mars near the Moon low to the West, after local sunrise.
Good luck, clear skies, and don’t miss this week’s unique, triple play dance of the Moon and Mars.
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