The most recent lunar occultation of Mars that was visible from the United States occurred on December 7, 2022. A handful of these events occur every few years around each Martian opposition, but they are usually only visible from a small portion of Earth, often over the ocean or in polar regions. The next lunar occultation of Mars visible across most of the United States will happen on the night of February 4–5, 2042. There are similar occultations of Mars in 2035, 2038, and 2039 visible in narrow swaths of South Florida and the Pacific Northwest.
This photo was taken with a handheld Canon 80D and a 600 mm lens. Settings were 1/2000 sec, f/8, ISO 400. The image was cropped and lightly edited in Adobe Lightroom.
The Moon also periodically covers Venus, Jupiter, Saturn, and the Solar System’s more distant planets. A good resource on lunar occultations is In-The-Sky.org, which lists events where the Moon will block out a planet or a bright star. Be sure you choose your location on the upper right corner of the page and toggle year by year to plan out future viewing opportunities.
Viewing these kinds of events can be breathtaking and humbling. In 2012, I was lucky enough to observe the transit of Venus in front of the Sun, something that only happens twice every 121 years.
Seeing Mars, twice the size of the Moon, rising above the lunar horizon like a rusty BB pellet next to a dusty volleyball provided a perfect illustration of the scale and grandeur of the Solar System. Similarly, viewing Venus dwarfed by the Sun was a revealing moment. The worlds accompanying Earth around the Sun are varied in size, shape, color, and composition.
In one glance, an observer can see the barren, airless lunar surface and a cold, desert planet that once harbored rivers, lakes, and potentially life, all while standing on our own planet, an oasis in the cosmos. One thing that connects them all is humanity’s quest for exploration. Today, robots are operating on or around the Moon and Mars. Governments and private companies are preparing to return astronauts to the lunar surface within a few years, then moving on to dispatch human expeditions to the red planet.
Plans to land astronauts on the Moon are already in motion, but significant financial and technological hurdles remain for a crew mission to put humans on Mars. But for a short time Monday night, it looked like there was a direct path.
“We want to have the quickest, cheapest way to get these 30 samples back.”
This photo montage shows sample tubes shortly after they were deposited onto the surface by NASA’s Perseverance Mars rover in late 2022 and early 2023. Credit: NASA/JPL-Caltech/MSSS
For nearly four years, NASA’s Perseverance rover has journeyed across an unexplored patch of land on Mars—once home to an ancient river delta—and collected a slew of rock samples sealed inside cigar-sized titanium tubes.
These tubes might contain tantalizing clues about past life on Mars, but NASA’s ever-changing plans to bring them back to Earth are still unclear.
On Tuesday, NASA officials presented two options for retrieving and returning the samples gathered by the Perseverance rover. One alternative involves a conventional architecture reminiscent of past NASA Mars missions, relying on the “sky crane” landing system demonstrated on the agency’s two most recent Mars rovers. The other option would be to outsource the lander to the space industry.
NASA Administrator Bill Nelson left a final decision on a new mission architecture to the next NASA administrator working under the incoming Trump administration. President-elect Donald Trump nominated entrepreneur and commercial astronaut Jared Isaacman as the agency’s 15th administrator last month.
“This is going to be a function of the new administration in order to fund this,” said Nelson, a former Democratic senator from Florida who will step down from the top job at NASA on January 20.
The question now is: will they? And if the Trump administration moves forward with Mars Sample Return (MSR), what will it look like? Could it involve a human mission to Mars instead of a series of robotic spacecraft?
The Trump White House is expected to emphasize “results and speed” with NASA’s space programs, with the goal of accelerating a crew landing on the Moon and sending people to explore Mars.
NASA officials had an earlier plan to bring the Mars samples back to Earth, but the program slammed into a budgetary roadblock last year when an independent review team concluded the existing architecture would cost up to $11 billion—double the previous cost projection—and wouldn’t get the Mars specimens back to Earth until 2040.
This budget and schedule were non-starters for NASA. The agency tasked government labs, research institutions, and commercial companies to come up with better ideas to bring home the roughly 30 sealed sample tubes carried aboard the Perseverance rover. NASA deposited 10 sealed tubes on the surface of Mars a couple of years ago as insurance in case Perseverance dies before the arrival of a retrieval mission.
“We want to have the quickest, cheapest way to get these 30 samples back,” Nelson said.
How much for these rocks?
NASA officials said they believe a stripped-down concept proposed by the Jet Propulsion Laboratory in Southern California, which previously was in charge of the over-budget Mars Sample Return mission architecture, would cost between $6.6 billion and $7.7 billion, according to Nelson. JPL’s previous approach would have put a heavier lander onto the Martian surface, with small helicopter drones that could pick up sample tubes if there were problems with the Perseverance rover.
NASA previously deleted a “fetch rover” from the MSR architecture and instead will rely on Perseverance to hand off sample tubes to the retrieval lander.
An alternative approach would use a (presumably less expensive) commercial heavy lander, but this concept would still utilize several elements NASA would likely develop in a more traditional government-led manner: a nuclear power source, a robotic arm, a sample container, and a rocket to launch the samples off the surface of Mars and back into space. The cost range for this approach extends from $5.1 billion to $7.1 billion.
Artist’s illustration of SpaceX’s Starship approaching Mars. Credit: SpaceX
JPL will have a “key role” in both paths for MSR, said Nicky Fox, head of NASA’s science mission directorate. “To put it really bluntly, JPL is our Mars center in NASA science.”
If the Trump administration moves forward with either of the proposed MSR plans, this would be welcome news for JPL. The center, which is run by the California Institute of Technology under contract to NASA, laid off 955 employees and contractors last year, citing budget uncertainty, primarily due to the cloudy future of Mars Sample Return.
Without MSR, engineers at the Jet Propulsion Laboratory don’t have a flagship-class mission to build after the launch of NASA’s Europa Clipper spacecraft last year. The lab recently struggled with rising costs and delays with the previous iteration of MSR and NASA’s Psyche asteroid mission, and it’s not unwise to anticipate more cost overruns on a project as complex as a round-trip flight to Mars.
Ars submitted multiple requests to interview Laurie Leshin, JPL’s director, in recent months to discuss the lab’s future, but her staff declined.
Both MSR mission concepts outlined Tuesday would require multiple launches and an Earth return orbiter provided by the European Space Agency. These options would bring the Mars samples back to Earth as soon as 2035, but perhaps as late as 2039, Nelson said. The return orbiter and sample retrieval lander could launch as soon as 2030 and 2031, respectively.
“The main difference is in the landing mechanism,” Fox said.
To keep those launch schedules, Congress must immediately approve $300 million for Mars Sample Return in this year’s budget, Nelson said.
NASA officials didn’t identify any examples of a commercial heavy lander that could reach Mars, but the most obvious vehicle is SpaceX’s Starship. NASA already has a contract with SpaceX to develop a Starship vehicle that can land on the Moon, and SpaceX founder Elon Musk is aggressively pushing for a Mars mission with Starship as soon as possible.
NASA solicited eight studies from industry earlier this year. SpaceX, Blue Origin, Rocket Lab, and Lockheed Martin—each with their own lander concepts—were among the companies that won NASA study contracts. SpaceX and Blue Origin are well-capitalized with Musk and Amazon’s Jeff Bezos as owners, while Lockheed Martin is the only company to have built a lander that successfully reached Mars.
This slide from a November presentation to the Mars Exploration Program Analysis Group shows JPL’s proposed “sky crane” architecture for a Mars sample retrieval lander. The landing system would be modified to handle a load about 20 percent heavier than the sky crane used for the Curiosity and Perseverance rover landings. Credit: NASA/JPL
The science community has long identified a Mars Sample Return mission as the top priority for NASA’s planetary science program. In the National Academies’ most recent decadal survey released in 2022, a panel of researchers recommended NASA continue with the MSR program but stated the program’s cost should not undermine other planetary science missions.
Teeing up for cancellation?
That’s exactly what is happening. Budget pressures from the Mars Sample Return mission, coupled with funding cuts stemming from a bipartisan federal budget deal in 2023, have prompted NASA’s planetary science division to institute a moratorium on starting new missions.
“The decision about Mars Sample Return is not just one that affects Mars exploration,” said Curt Niebur, NASA’s lead scientist for planetary flight programs, in a question-and-answer session with solar system researchers Tuesday. “It’s going to affect planetary science and the planetary science division for the foreseeable future. So I think the entire science community should be very tuned in to this.”
Rocket Lab, which has been more open about its MSR architecture than other companies, has posted details of its sample return concept on its website. Fox declined to offer details on other commercial concepts for MSR, citing proprietary concerns.
“We can wait another year, or we can get started now,” Rocket Lab posted on X. “Our Mars Sample Return architecture will put Martian samples in the hands of scientists faster and more affordably. Less than $4 billion, with samples returned as early as 2031.”
Through its own internal development and acquisitions of other aerospace industry suppliers, Rocket Lab said it has provided components for all of NASA’s recent Mars missions. “We can deliver MSR mission success too,” the company said.
Rocket Lab’s concept for a Mars Sample Return mission. Credit: Rocket Lab
Although NASA’s deferral of a decision on MSR to the next administration might convey a lack of urgency, officials said the agency and potential commercial partners need time to assess what roles the industry might play in the MSR mission.
“They need to flesh out all of the possibilities of what’s required in the engineering for the commercial option,” Nelson said.
On the program’s current trajectory, Fox said NASA would be able to choose a new MSR architecture in mid-2026.
Waiting, rather than deciding on an MSR plan now, will also allow time for the next NASA administrator and the Trump White House to determine whether either option aligns with the administration’s goals for space exploration. In an interview with Ars last week, Nelson said he did not want to “put the new administration in a box” with any significant MSR decisions in the waning days of the Biden administration.
One source with experience in crafting and implementing US space policy told Ars that Nelson’s deferral on a decision will “tee up MSR for canceling.” Faced with a decision to spend billions of dollars on a robotic sample return or billions of dollars to go toward a human mission to Mars, the Trump administration will likely choose the latter, the source said.
If that happens, NASA science funding could be freed up for other pursuits in planetary science. The second priority identified in the most recent planetary decadal survey is an orbiter and atmospheric probe to explore Uranus and its icy moons. NASA has held off on the development of a Uranus mission to focus on the Mars Sample Return first.
Science and geopolitics
Whether it’s with robots or humans, there’s a strong case for bringing pristine Mars samples back to Earth. The titanium tubes carried by the Perseverance rover contain rock cores, loose soil, and air samples from the Martian atmosphere.
“Bringing them back will revolutionize our understanding of the planet Mars and indeed, our place in the solar system,” Fox said. “We explore Mars as part of our ongoing efforts to safely send humans to explore farther and farther into the solar system, while also … getting to the bottom of whether Mars once supported ancient life and shedding light on the early solar system.”
Researchers can perform more detailed examinations of Mars specimens in sophisticated laboratories on Earth than possible with the miniature instruments delivered to the red planet on a spacecraft. Analyzing samples in a terrestrial lab might reveal biosignatures, or the traces of ancient life, that elude detection with instruments on Mars.
“The samples that we have taken by Perseverance actually predate—they are older than any of the samples or rocks that we could take here on Earth,” Fox said. “So it allows us to kind of investigate what the early solar system was like before life began here on Earth, which is amazing.”
Fox said returning Mars samples before a human expedition would help NASA prioritize where astronauts should land on the red planet.
In a statement, the Planetary Society said it is “concerned that NASA is again delaying a decision on the program, committing only to additional concept studies.”
“It has been more than two years since NASA paused work on MSR,” the Planetary Society said. “It is time to commit to a path forward to ensure the return of the samples already being collected by the Perseverance rover.
“We urge the incoming Trump administration to expedite a decision on a path forward for this ambitious project, and for Congress to provide the funding necessary to ensure the return of these priceless samples from the Martian surface.”
China says it is developing its own mission to bring Mars rocks back to Earth. Named Tianwen-3, the mission could launch as soon as 2028 and return samples to Earth by 2031. While NASA’s plan would bring back carefully curated samples from an expansive environment that may have once harbored life, China’s mission will scoop up rocks and soil near its landing site.
“They’re just going to have a mission to grab and go—go to a landing site of their choosing, grab a sample and go,” Nelson said. “That does not give you a comprehensive look for the scientific community. So you cannot compare the two missions. Now, will people say that there’s a race? Of course, people will say that, but it’s two totally different missions.”
Still, Nelson said he wants NASA to be first. He said he has not had detailed conversations with Trump’s NASA transition team.
“I think it was a responsible thing to do, not to hand the new administration just one alternative if they want to have a Mars Sample Return,” Nelson said. “I can’t imagine that they don’t. I don’t think we want the only sample return coming back on a Chinese spacecraft.”
Stephen Clark is a space reporter at Ars Technica, covering private space companies and the world’s space agencies. Stephen writes about the nexus of technology, science, policy, and business on and off the planet.
Eleven months after the Ingenuity helicopter made its final flight on Mars, engineers and scientists at NASA and a private company that helped build the flying vehicle said they have identified what probably caused it to crash on the surface of Mars.
In short, the helicopter’s on-board navigation sensors were unable to discern enough features in the relatively smooth surface of Mars to determine its position, so when it touched down, it did so moving horizontally. This caused the vehicle to tumble, snapping off all four of the helicopter’s blades.
Delving into the root cause
It is not easy to conduct a forensic analysis like this on Mars, which is typically about 100 million miles from Earth. Ingenuity carried no black box on board, so investigators have had to piece together their findings from limited data and imagery.
“While multiple scenarios are viable with the available data, we have one we believe is most likely: Lack of surface texture gave the navigation system too little information to work with,” saidIngenuity’s first pilot, Håvard Grip of NASA’s Jet Propulsion Laboratory, in a news release.
A team from NASA and a company that specializes in unmanned aerial vehicles, AeroVironment, started by looking at the terrain where Ingenuity was operating over during its 72nd flight, on January 18 of this year. The helicopter’s navigation system tracked visual features on the surface using a downward-looking camera. During its initial flights, Ingenuity was able to discern pebbles and other features to determine its position. But nearly three years later, Ingenuity was flying in a region of Jezero Crater filled with steep, relatively featureless sand ripples.
Enlarge/ A “selfie” photo of China’s Zhurong rover and the Tianwen-1 landing platform on Mars in 2021.
China plans to launch two heavy-lift Long March 5 rockets with elements of the Tianwen-3 Mars sample return mission in 2028, the mission’s chief designer said Thursday.
In a presentation at a Chinese space exploration conference, the chief designer of China’s robotic Mars sample return project described the mission’s high-level design and outlined how the mission will collect samples from the Martian surface. Reports from the talk published on Chinese social media and by state-run news agencies were short on technical details and did not discuss any of the preparations for the mission.
Public pronouncements by Chinese officials on future space missions typically come true, but China is embarking on challenging efforts to explore the Moon and Mars. China aims to land astronauts on the lunar surface by 2030 in a step toward eventually building a Moon base called the International Lunar Research Station.
Liu Jizhong, chief designer of the Tianwen-3 mission, did not say when China could have Mars samples back on Earth. In past updates on the Tianwen-3 mission, the launch date has alternated between 2028 and 2030, and officials previously suggested the round-trip mission would take about three years. This would suggest Mars rocks could return to Earth around 2031, assuming an on-time launch in 2028.
NASA, meanwhile, is in the middle of revamping its architecture for a Mars sample return mission in cooperation with the European Space Agency. In June, NASA tapped seven companies, including SpaceX and Blue Origin, to study ways to return Mars rocks to Earth for less than $11 billion and before 2040, the cost and schedule for NASA’s existing plan for Mars sample return.
That is too expensive and too long to wait for Mars sample return, NASA Administrator Bill Nelson said in April. Mars sample return is the highest priority for NASA’s planetary science division and has been the subject of planning for decades. The Perseverance rover currently on Mars is gathering several dozen specimens of rock powder, soil, and Martian air in cigar-shaped titanium tubes for eventual return to Earth.
This means China has a shot at becoming the first country to bring pristine samples from Mars back to Earth, and China doesn’t intend to stop there.
“If all the missions go as planned, China is likely to become the first country to return samples from Mars,” said Wu Weiren, chief designer of China’s lunar exploration program, in a July interview with Chinese state television. “And we will explore giant planets, such as Jupiter. We will also explore some of the asteroids, including sample return missions from an asteroid, and build an asteroid defense system.”
The asteroid sample return mission is known as Tianwen-2, and is scheduled for launch next year. Tianwen means “questions to heaven.”
China doesn’t have a mission currently on Mars gathering material for its Tianwen-3 sample return mission. The country’s first Mars mission, Tianwen-1, landed on the red planet in May 2021 and deployed a rover named Zhurong. China’s space agency hasn’t released any update on the rover since 2022, suggesting it may have succumbed to the harsh Martian winter.
So, the Tianwen-3 mission must carry everything it needs to land on Mars, collect samples, package them for return to Earth, and then launch them from the Martian surface back into space. Then, the sample carrier will rendezvous with a return vehicle in orbit around Mars. Once the return spacecraft has the samples, it will break out of Mars orbit, fly across the Solar System, and release a reentry capsule to bring the Mars specimens to the Earth.
All of the kit for the Tianwen-3 mission will launch on two Long March 5 rockets, the most powerful operational launcher in China’s fleet. One Long March 5 will launch the lander and ascent vehicle, and another will propel the return spacecraft and Earth reentry capsule toward Mars.
Liu, Tianwen-3’s chief designer, said an attempt to retrieve samples from Mars is the most technically challenging space exploration mission since the Apollo program, according to China’s state-run Xinhua news agency. Liu said China will adhere to international agreements on planetary protection to safeguard Mars, Earth, and the samples themselves from contamination. The top scientific goal of the Tianwen-3 mission is to search for signs of life, he said.
Tianwen-3 will collect samples with a robotic arm and a subsurface drill, and Chinese officials previously said the mission may carry a helicopter and a mobile robot to capture more diverse Martian materials farther away from the stationary lander.
Liu said China is open to putting international payloads on Tianwen-3 and will collaborate with international scientists to analyze the Martian samples the mission returns to Earth. China is making lunar samples returned by the Chang’e 5 mission available for analysis by international researchers, and Chinese officials have said they anticipate a similar process to loan out samples from the far side of the Moon brought home by the Chang’e 6 mission earlier this year.
Enlarge/ The two spacecraft for NASA’s ESCAPADE mission at Rocket Lab’s factory in Long Beach, California.
Two NASA spacecraft built by Rocket Lab are on the road from California to Florida this weekend to begin preparations for launch on Blue Origin’s first New Glenn rocket.
These two science probes must launch between late September and mid-October to take advantage of a planetary alignment between Earth and Mars that only happens once every 26 months. NASA tapped Blue Origin, Jeff Bezos’ space company, to launch the Escape and Plasma Acceleration and Dynamics Explorers (ESCAPADE) mission with a $20 million contract.
Last November, the space agency confirmed the $79 million ESCAPADE mission will launch on the inaugural flight of Blue Origin’s New Glenn rocket. With this piece of information, the opaque schedule for Blue Origin’s long-delayed first New Glenn mission suddenly became more clear.
The launch period opens on September 29. The two identical Mars-bound spacecraft for the ESCAPADE mission, nicknamed Blue and Gold, are now complete. Rocket Lab announced Friday that its manufacturing team packed the satellites and shipped them from their factory in Long Beach, California. Over the weekend, they arrived at a clean room facility just outside the gates of NASA’s Kennedy Space Center in Florida, where technicians will perform final checkups and load hydrazine fuel into both spacecraft, each a little more than a half-ton in mass.
Then, if Blue Origin is ready, ground teams will connect the ESCAPADE spacecraft with the New Glenn’s launch adapter, encapsulate the probes inside the payload fairing, and mount them on top of the rocket.
“There’s a whole bunch of checking and tests to make sure everything’s OK, and then we move into fueling, and then we integrate with the launch vehicle. So it’s a big milestone,” said Rob Lillis, the mission’s lead scientist from the University of California Berkeley’s Space Science Laboratory. “There have been some challenges along the way. This wasn’t easy to make happen on this schedule and for this cost. So we’re very happy to be where we are.”
Racing to the finish line
But there’s a lot for Blue Origin to accomplish in the next couple of months if the New Glenn rocket is going to be ready to send the ESCAPADE mission toward Mars in this year’s launch period. Blue Origin has not fully exercised a New Glenn rocket during a launch countdown, hasn’t pumped a full load of cryogenic propellants into the launch vehicle, and hasn’t test-fired a full complement of first stage or second stage engines.
These activities typically take place months before the first launch of a large new orbital-class rocket. For comparison, SpaceX test-fired its first fully assembled Falcon 9 rocket on the launch pad about three months before its first flight in 2010. United Launch Alliance completed a hot-fire test of its new Vulcan rocket on the launch pad last year, about seven months before its inaugural flight.
However, Blue Origin is making visible progress toward the first flight of New Glenn, after years of speculation and few outward signs of advancement. Earlier this year, the company raised a full-scale, 320-foot-tall (98-meter) New Glenn rocket on its launch pad at Cape Canaveral Space Force Station and loaded it with liquid nitrogen, a cryogenic substitute for the methane and liquid hydrogen fuel it will burn in flight.
Enlarge/ NASA’s Perseverance rover discovered “leopard spots” on a reddish rock nicknamed “Cheyava Falls” in Mars’ Jezero Crater in July 2024.
NASA/JPL-Caltech/MSSS
NASA’s Perseverance rover has found a very intriguing rock on the surface of Mars.
An arrowhead-shaped rock observed by the rover has chemical signatures and structures that could have been formed by ancient microbial life. To be absolutely clear, this is not irrefutable evidence of past life on Mars, when the red planet was more amenable to water-based life billions of years ago. But discovering these colored spots on this rock is darn intriguing and has Mars scientists bubbling with excitement.
“These spots are a big surprise,” said David Flannery, an astrobiologist and member of the Perseverance science team from the Queensland University of Technology in Australia, in a NASA news release. “On Earth, these types of features in rocks are often associated with the fossilized record of microbes living in the subsurface.”
What the rover found
This is a very recent discovery, and the science has not yet been peer-reviewed. The sample was collected on July 21—a mere four days ago—as the rover explored the Neretva Vallis riverbed. This valley was formed long ago when water rushed into Jezero Crater.
The science team operating Perseverance has nicknamed the rock Chevaya Falls and subjected it to multiple scans by the rover’s SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instrument. The distinctive colorful spots, containing both iron and phosphate, are a smoking gun for certain chemical reactions—rather than microbial life itself.
On Earth, microbial life can derive energy from these kinds of chemical reactions. So, what we have here is a plausible source of energy for microbes on Mars. In addition, there are organic chemicals present on the same rock, which is consistent with something living there. From this, it is tempting to jump to the idea of microbes living on a rock, eons ago, in a Martian river. But this is not direct evidence of life.
NASA has a seven-step process for determining whether something can be confirmed as extraterrestrial life. This is known as the CoLD scale, for Confidence of Life Detection. In this case, the detection of these spots on a Martian rock represents just the first of seven steps—for example, scientists must still rule out non-biological possibility and identify other signals to have confidence in off-world life.
Bring them home
According to NASA, Perseverance has used all of its available instrumentation to study Chevaya Falls. “We have zapped that rock with lasers and X-rays and imaged it literally day and night from just about every angle imaginable,” said Ken Farley, Perseverance project scientist. “Scientifically, Perseverance has nothing more to give.”
The discovery provides some wind in the sails for NASA’s flagging efforts to devise and fly a Mars Sample Return mission. The agency’s most recent plan, costing $11 billion, was determined to be too expensive. Now, the space agency is asking the industry for help. In June it commissioned 10 studies on alternative means of returning rocks from Mars sooner, and presumably for a lower cost.
Now, scientists can point to rocks like Chevaya Falls and say this is precisely why they must be studied in ultra-capable labs back on Earth.
Meteorites crash down to Mars every day. After analyzing data from NASA’s InSight lander, an international team of researchers noticed that its seismometer, SEIS, detected six nearby seismic events. These were linked to the same acoustic atmospheric signal that meteorites generate when whizzing through the atmosphere of Mars. Further investigation identified all six as part of an entirely new class of quakes known as VF (very high frequency) events.
The collisions that generate VF marsquakes occur in fractions of a second, much less time than the few seconds it takes tectonic processes to cause quakes similar in size. This is some of the key seismological data that has helped us understand the occurrence of earthquakes caused by meteoric impacts on Mars. This is also the first time seismic data was used to determine how frequently impact craters are formed.
“Although a non-impact origin cannot be definitively excluded for each VF event, we show that the VF class as a whole is plausibly caused by meteorite impacts,” the researchers said in a study recently published in Nature.
Seismic shift
Scientists had typically determined the approximate meteorite impact rate on Mars by comparing the frequency of craters on its surface to the expected rate of impacts calculated using counts of lunar craters that were left behind by meteorites. Models of the lunar cratering rate were then adjusted to fit Martian conditions.
Looking to the Moon as a basis for comparison was not ideal, as Mars is especially prone to being hit by meteorites. The red planet is not only a more massive body that has greater gravitational pull, but it is located near the asteroid belt.
Another issue is that lunar craters are often better preserved than Martian craters because there is no place in the Solar System dustier than Mars. Craters in orbital images are often partly obscured by dust, which makes them difficult to identify. Sandstorms can complicate matters by covering craters in more dust and debris (something that cannot occur on the Moon due to the absence of wind).
InSight deployed its SEIS instrument after it landed in the Elysium Planitia region of Mars. In addition to detecting tectonic activity, the seismometer can potentially determine the impact rate through seismic data. When meteorites strike Mars, they produce seismic waves just like tectonic marsquakes do, and the waves can be detected by seismometers when they travel through the mantle and crust. An immense quake picked up by SEIS was linked to a crater 150 meters (492 feet) wide. SEIS would later detect five more marsquakes that were all associated with an acoustic signal (detected by a different sensor on InSight) that is a telltale sign of a falling meteorite.
A huge impact
Something else stood out about the six impact-driven marsquakes detected with seismic data. Because of the velocity of meteorites (over 3,000 meters or 9,842 feet per second), these events happened faster than any other type of marsquake, even faster than quakes in the high frequency (HF) class. That’s how they earned their own classification: very high frequency, or VF, quakes. When the InSight team used the Mars Reconnaissance Orbiter’s (MRO) Context Camera (CTX) to image the locations of the events picked up by SEIS, there were new craters present in the images.
There are additional seismic events that haven’t been assigned to craters yet. They are thought to be small craters formed by meteorites about the size of basketballs, which are extremely difficult to see in orbital images from MRO.
The researchers were able to use SEIS data to estimate the diameters of craters based on distance from InSight (according to how long it took seismic waves to reach the spacecraft) and the magnitude of the VF marsquakes associated with them. They were also able to derive the frequency of quakes picked up by SEIS. Once a frequency estimate based on the data was applied to the entire surface area of Mars, they estimated that around 280 to 360 VF quakes occur each year.
“The case is strong that the unique VF marsquake class is consistent with impacts,” they said in the same study. “It is, therefore, worthwhile considering the implications of attributing all VF events to meteoroid impacts.”
Their detection has added to the estimated number of impact craters on Mars since many could not be seen from space before. What can VF impacts tell us? The impact rate on a planet or moon is important for determining the age of that object’s surface. Using impacts has helped us determine that the surface of Venus is constantly being renewed by volcanic activity, while most of the surface of Mars has not been covered in lava for billions of years.
Figuring out the rate of meteorite impacts can also help protect spacecraft and, someday, maybe Martian astronauts, from potential hazards. The study suggests that there are periods where impacts are more or less frequent, so it might be possible to predict when the sky is a bit more likely to be clear of falling space rocks—and when it isn’t. Meteorites are not much of a danger to Earth since most of them burn up in the atmosphere. Mars has a much thinner atmosphere that more can make it through, and there is no umbrella for a meteor shower.
Mars has a history of liquid water on its surface, including lakes like the one that used to occupy Jezero Crater, which have long since dried up. Ancient water that carried debris—and melted water ice that presently does the same—were also thought to be the only thing driving the formation of gullies spread throughout the Martian landscape. That view may now change thanks to new results that suggest dry ice can also shape the landscape.
It’s sublime
Previously, scientists were convinced that only liquid water shaped gullies on Mars because that’s what happens on Earth. What was not taken into account was sublimation, or the direct transition of a substance from a solid to a gaseous state. Sublimation is how CO2 ice disappears (sometimes water ice experiences this, too).
Frozen carbon dioxide is everywhere on Mars, including in its gullies. When CO2 ice sublimates on one of these gullies, the resulting gas can push debris further down the slope and continue to shape it.
Led by planetary researcher Lonneke Roelofs of Utrecht University in the Netherlands, a team of scientists has found that the sublimation of CO2 ice could have shaped Martian gullies, which might mean the most recent occurrence of liquid water on Mars may have been further back in time than previously thought. That could also mean the window during which life could have emerged and thrived on Mars was possibly smaller.
“Sublimation of CO2 ice, under Martian atmospheric conditions, can fluidize sediment and creates morphologies similar to those observed on Mars,” Roelofs and her colleagues said in a study recently published in Communications Earth & Environment.
Into thin air
Earth and Martian gullies have basically the same morphology. The difference is that we’re certain that liquid water is behind their formation and continuous shaping and re-shaping on Earth. Such activity includes new channels being carved out and more debris being taken to the bottom.
While ancient Mars may have had enough stable liquid water to pull this off, there is not enough on the present surface of Mars to sustain that kind of activity. This is where sublimation comes in. CO2 ice has been observed on the surface of Mars at the same time that material starts flowing.
After examining observations like these, the researchers hypothesized these flows are pushed downward by gas as the frozen carbon dioxide sublimates. Because of the low pressure on Mars, sublimation creates a relatively greater gas flux than it would on Earth—enough power to make fluid motion of material possible.
There are two ways sublimation can be triggered to get these flows moving. When part of a more exposed area of a gully collapses, especially on a steep slope, sediment and other debris that have been warmed by the Sun can fall on CO2 ice in a shadier and cooler area. Heat from the falling material could supply enough energy for the frost to sublimate. Another possibility is that CO2 ice and sediment can break from the gully and fall onto warmer material, which will also trigger sublimation.
Mars in a lab
There is just one problem with these ideas: since humans have not landed on Mars (yet), there are no in situ observations of these phenomena, only images and data beamed back from spacecraft. So, everything is hypothetical. The research team would have to model Martian gullies to watch the action in real time.
To re-create a part of the red planet’s landscape in a lab, Roelofs built a flume in a special environmental chamber that simulated the atmospheric pressure of Mars. It was steep enough for material to move downward and cold enough for CO2 ice to remain stable. But the team also added warmer adjacent slopes to provide heat for sublimation, which would drive movement of debris. They experimented with both scenarios that might happen on Mars: heat coming from beneath the CO2 ice and warm material being poured on top of it. Both produced the kinds of flows that had been hypothesized.
For further evidence that flows driven by sublimation would happen under certain conditions, two further experiments were conducted, one under Earth-like pressures and one without CO2 ice. No flows were produced by either.
“For the first time, these experiments provide direct evidence that CO2 sublimation can fluidize, and sustain, granular flows under Martian atmospheric conditions,” the researchers said in the study.
Because this experiment showed that gullies and systems like them can be shaped by sublimation and not just liquid water, it raises questions about how long Mars had a sufficient supply of liquid water on the surface for any organisms (if they existed at all) to survive. Its period of habitability might have been shorter than it was once thought to be. Does this mean nothing ever lived on Mars? Not necessarily, but Roelofs’ findings could influence how we see planetary habitability in the future.
Enlarge/ Ship 28, the Starship for SpaceX’s next full-scale test flight, fires up one of its engines on December 29 in Texas.
SpaceX
It’s no secret that Elon Musk has big ambitions for SpaceX’s Starship mega-rocket. This is the vehicle that, with plenty of permutations and upgrades, Musk says will ferry cargo and people across the Solar System to build a settlement on Mars, making humanity a multi-planetary species and achieving the billionaire’s long-standing dream.
Of course, that is a long way off. SpaceX is still working on getting Starship into orbit or close to it, an achievement that appears to be possible this year. Then, the company will start launching Starlink satellites on Starship missions while testing in-space refueling technology needed to turn Starship into a human-rated Moon lander for NASA.
SpaceX’s South Texas team is progressing toward the third full-scale Starship test flight. On December 20, the Starship’s upper stage slated for the next test flight completed a test-firing of its Raptor engines at the Starbase launch site on the Texas Gulf Coast. Nine days later, the 33-engine Super Heavy booster fired up on the launch pad for its own static fire test. On the same day, SpaceX hot-fired the Starship upper stage once again on a test stand next to the launch pad.
With those milestones complete, ground teams rolled the booster back to its hangar for final preflight checks and reconfigurations. The ship, too, will need to be rolled back to its high bay.
SpaceX could be weeks away from having both vehicles ready to fly, but the company hasn’t released an update on lessons learned from the previous Starship test flight in November. That flight was largely successful, with apparently flawless performance from the 33 engines on the Super Heavy booster during launch. The Starship upper stage reached space before self-destructing downrange over the Gulf of Mexico. The booster exploded during a maneuver to bring itself back to Earth for a controlled splashdown at sea.
The company’s engineers will want to understand and correct whatever caused those issues. The Federal Aviation Administration then needs to approve SpaceX’s investigation into the last Starship flight before issuing a new commercial launch license. When it flies again, Starship will try to reach near orbital velocity, enough speed to travel most of the way around the world before reentering the atmosphere near Hawaii.
Verifying the performance of Starship’s heat shield tiles during reentry will be valuable learning for SpaceX, but Starship first needs to be fully successful with a launch. This is just the start for the privately funded Starship program.
