Building with Legos is a favored pastime for many small children and adults. We’ve even covered some more space-oriented Lego sets here at UT. But, as the Lego movie points out, they constitute “a highly sophisticated interlocking brick system.” So why not take the idea underpinning Legos – that you can make anything you want out of a set of generic pieces and apply it to a much more serious scientific topic…like robots.
That is precisely what a student-led team from MIT has done with the Walking Oligometric Robotic Mobility Systems (WORMS) robot they have developed. Conceived initially as a project in response to NASA’s Breakthrough, Innovative, and Game-changing (BIG) idea challenge, the system is designed to have replaceable parts to achieve various mobility tasks over rugged terrain.
Part of its appeal is its lack of wheels. Despite its name, WORMS looks more like a spider, at least in the configuration that has been the most thoroughly tested. The design team, based out of the Space Resources Workshop, took biological inspiration from several different creatures, including spiders, elephants, and oxen. Each could be used for a specific task – spiders could explore caves, elephants could join together to transport heavy objects, and oxen could drag other equipment up or down steep slopes.
At the heart of the system is a core that could easily snap different parts onto it. If a spider bot is needed to explore a lava tube, six legs could be snapped on, along with a drill to dig for liquid water. Suppose the astronauts programming the robots needed to get a solar panel up to the top of a ridgeline to collect more sunlight. In that case, they could configure the robot with many more legs and even multiple central cores, allowing the WORMS system to expand its payload capacity linearly.
In place of wheels, the WORMS team uses articulated appendages measuring about 1 meter in length and with a part that looks somewhat like Captain America’s shield in place of a foot. However, like much of the rest of the system, those parts can be replaced with differing parts for different use cases. Many could be 3D printed on the Moon itself using one of the various lunar 3D printing technologies we discussed in past articles.
For now, the WORMS remains Earthbound but is still under active development. A paper from the group recently won the Best Paper award at the Institute for Electrical Engineers’ Aerospace Conference. With continued support and a never-ending stream of MIT students interested in continuing development on the project, what started as a student-led project could morph into a fully fleshed-out robotic support system for the Moon’s first long-term inhabitants.
UT video on lunar lava tubes, where WORMS or other robotic explorers could potentially be the first to tread.
When the Artemis astronauts and future explorers go to the Moon and Mars, they’ll need power. Lots of it. Of course, they’ll use solar panels to generate the juice they need for habitats, experiments, rovers, and so on. But, they’ll need batteries for power storage. Those things weigh a lot and cost a fortune to send up from Earth. So, why not simply 3D print their own when they get there?
That’s the question a team of researchers at the University of Texas at El Paso (UTEP) and Youngstown State University (YSU) are working to answer. They’ve teamed up with several NASA centers in a $2.5 million project to explore the idea of 3D printing batteries using local materials.
“UTEP is a seminal partner in this NASA-led project with our long and deep heritage in additive manufacturing,” said Eric MacDonald, professor of aerospace and mechanical engineering and associate dean in the UTEP College of Engineering. “UTEP’s reputation in 3D printing, material science, and our state-of-the-art facilities were important factors in convincing our NASA partners to pursue this potentially transformative research – for space exploration but for terrestrial applications of batteries as well.”
UTEP has joined a project led by NASA to leverage 3D-printing processes with the aim of manufacturing rechargeable batteries using lunar and Martian regolith. Photo by JR Hernandez / UTEP Marketing and Communications
This NASA-led effort is a big step toward adapting the 3D print process for space use. Another goal is to be able to extrude batteries in about any shape needed. Then, they can be fitted into walls of habitats or inside other equipment to save space. And, if it works out, eventually astronauts will be able to print habitat modules, power generators, and other facilities.
What Kind of 3D Print Process to Use in Space?
The project is looking at two types of 3D print methods. One is called “material extrusion”, where the shapes are pushed out of the printer in their final form. The other is “vat photopolymerization” (VPP). The basic material is a vat of liquid photopolymer resin. The machine then uses this material to construct an object, layer by layer. VPP would allow lunar inhabitants to make shape-conformable batteries to fit wherever they’re needed. That includes smaller spacecraft, robots, portable power units, and large-scale long-term power systems.
Illustration representing materials extraction and manufacturing of rechargeable batteries using lunar and martian materials as material feedstock for 3D printers. This original artwork was conceived, created, and adapted by A. Maurel, with a contribution from P. Garcia to the central diagram that includes the 3D printer. Credit NASA.
Making batteries using local regolith puts an interesting limitation on what type can be printed. Right now, on the International Space Station, the primary power systems rely on lithium-ion power storage units brought up from Earth. Unfortunately, if people are going to manufacture power storage units on the Moon or Mars, they aren’t going to be able to use lithium-ion. That’s because there’s very little lithium available to mine on the Moon and Mars. So, what will they use?
The NASA and university teams are looking at sodium-ion technology. Both the Moon and Mars do have some amounts of sodium accessible. So, the UTEP research team will be studying sodium-ion battery chemistry and possible printing solutions. After that, they’ll test the procedures.
Lunar and Martian Batteries Tech
NASA, UTEP, and YSU will also work on the extraction of battery materials and precursors for these sodium-ion batteries from lunar and Martian regolith. The university teams already developed and used VPP 3D printing to make composite resin feedstocks for each part of the proposed power storage units. Technically, that includes the electrodes, electrolytes, and current collectors. The team at NASA’s Marshall Ames centers developed and ME 3D printed composite inks for the different battery components. UTEP and NASA’s Glenn Research Center will electrochemically test the completed 3D-printed sodium-ion battery components.
“This project with NASA is an opportunity to demonstrate UTEP’s expertise in both energy storage and 3D printing,” said Alexis Maurel of the UTEP Department of Aerospace and Mechanical Engineering. “Additive manufacturing appears as a unique approach to manufacture shape-conformable batteries to support human operations in space and on the surface of the moon or Mars, where cargo resupply is not as readily available.”
This past summer (June 14th to June 16th), representatives from the public space sector, the commercial space industry, and academic institutions convened at George Washington University in Washington D.C. for The Ninth Community Workshop for Achievability and Sustainability of Human Exploration of Mars. The invitation-only event was hosted by Explore Mars, Inc., a non-profit organization dedicated to fostering international collaboration and cooperation between government and industry to achieve the human exploration of Mars by the 2030s.
The purpose of this workshop is to identify activities that will help prepare for missions to Mars by the 2030s. In particular, the workshop sought to address how a sustainable program of human Martian exploration can be achieved. The highlights of this event were recently shared with the release of the Achieve Mars (AM) IX Report, which established priorities and science objectives for future missions to Mars. The authors also made several recommendations for how cutting-edge technologies could play a role, how the health and safety of astronauts can be assured, and how Mars and Earth can be protected from possible contamination.
The Report emphasizes that a plan is needed to implement a cohesive campaign of robotic and human explorers on Mars. This campaign must leverage near-term activities in Low Earth Orbit (LEO) – i.e., aboard the International Space Station (ISS) – and the cis-lunar system to develop the necessary expertise and validate key systems. This is consistent with the objectives of NASA’s Artemis Program, which aims to establish a program of “sustained lunar exploration and development.” This includes the Lunar Gateway in orbit and the Artemis Base Camp on the surface to facilitate lunar exploration in this decade and crewed missions to Mars in the next.
An artist’s concept of Mars explorers and their habitat on the Red Planet. Credit: NASA
The authors also call for preparatory work to be done that will address the issues of human health and performance, science priorities, transit, surface operations strategies, proposed technological solutions, timelines for development and deployment, and eventual missions. As expected, there were many interesting takeaways from this four-day workshop and its many sessions. Janet Ivey, creator and CEO of the educational program Janet’s Planet and the President of Explore Mars, shared her thoughts on AM IX with Universe Today via phone:
“Most profound to me is the talent and the genius that is behind creating these systems, having these conversations, thinking about these long poles of architecture, how we get humans from Earth to Mars safely so that research could be done. How we could see long-term, working, living, and thriving on Mars in our future. They present some profound and stunning arguments for doing things the way they see them happening.
“For me, it’s the fact that you have people together attempting to discern what is something that is still unknowable. We have rockets, we have spacecraft, and we have landers. But how do we do this safely and sustainably to protect our most precious resource, which is humans? To sit in a room with specialists who can come up with actionable solutions for these challenges, how do we live and work on Mars – that is amazing to me.”
The four-day workshop saw many experts across multiple disciplines address the most pressing issues of Martian exploration and made some interesting recommendations. Here are some of the biggest takeaways from the AM IX, according to the Report:
Getting There
A major focus was on how the first crewed missions to Mars would make the transit there and back. This is a major challenge considering that missions to Mars must launch every 26 months to coincide with a Mars Opposition (when Earth and Mars are closest). Using conventional methods and propellants, the estimated transit time could be anywhere from six to nine months. This presents numerous challenges for astronaut health due to long-term exposure to radiation, microgravity, and the need for adequate supplies. For this reason, the Report stresses the need for a “Mars Campaign” rather than individual non-defined missions:
“This means a program (cadence) of robotic and human missions, starting with better-defined links between Artemis and future Mars missions. It was agreed that the opportunities offered by the 2033 launch window are not to be dismissed lightly (assuming crew readiness), but no consensus was reached as to the value of an initial orbital mission, and no consensus was reached on an initial conjunction vs. opposition mission.”
Artist’s concept of a Bimodal Nuclear Thermal Propulsion (NTP) system in Low Earth Orbit. Credit: NASA
As expected, Nuclear-Thermal and Nuclear-Electric Propulsion (NTP/NEP) was suggested as a solution. This technology is currently being investigated by NASA’s Advanced Innovation Concepts (NAIC) program, and the agency has partnered with DARPA to test an NTP concept in space by early 2027. However, these recommendations (according to the Report) “were met with both enthusiasm and skepticism.” On the enthusiastic side, the advantages of power density, specific impulse, reduced mass, and reduced transit times (45 to 100 days) were undoubtedly cited as reasons for adoption.
On the skeptical side, the Report indicates that some attendees “cited studies that suggested neither NTP nor NEP would be available in the human exploration time horizon of interest.” Therefore, the Report recommended that NASA should not commit to NTP/NEP methods for crewed missions to Mars without further study. As Joe Cassady, the Executive V.P. of Explore Mars and the Executive Director of Space Programs at Aerojet Rocketdyne, told Universe Today via email:
“I think our workshop supported NASA’s continued work on space nuclear propulsion. Our only caveat was that we thought some missions could be done without the need to have a fully developed NTP/NEP system. In other words, we don’t have to wait until those are done to start sending human missions to Mars.”
The role of SpaceX’s future workhorse, the Starship and Super-Heavy launch vehicle, was also the subject of discussion. As the attendees noted, the launch system’s main benefit is that it promises a major reduction in the cost per pound of sending payloads to orbit, the Moon, and ultimately to Mars. However, there are some caveats and addendums regarding certain “engineering demonstrations” that are yet to be performed. These included “on-orbit refueling and ISRU [in-situ resource utilization] at a scale required by the Starship.”
Health and Safety
The Report acknowledges that ISS Expeditions lasting between six months and a year have yielded valuable data and insight into how time in space affects human physiology. However, this information is limited regarding missions that are longer in duration and involve traveling to locations in deep space. As a result, they emphasize how new human health performance system guidelines need to be established that include methods for maintaining astronaut health for missions lasting up to three years – including transits and while operating in the hostile environment of Mars.
The Goldstone Deep Space Communications Complex, situated in the Mojave Desert in California. Credit: NASA
First, there’s the need for a certifiable system that can store (and/or produce) food and maintain its freshness and nutritional value for up to three years. The wording of this suggests that either a robust supply cache is needed or am amply of greens and vegetable proteins can be grown aboard the spacecraft (similar to what is done aboard the ISS). In addition, they made several recommendations to ensure the psychological well-being of astronauts, including:
“[A]dequate downtime for the crew, family support communications from Earth, and a well-conceived wellness plan that provides both physical and psychological support. This includes refresher training, privacy in sleep quarters, entertainment opportunities, etc., to build crew cohesion and ensuring that the crew has meaningful work to perform during transit.”
The Report emphasizes the need for mobility systems that can extend exploration, achieve scientific objectives, and allow the crew to transfer between landed elements (i.e., between the lander and the habitat, between surface stations, etc.) without difficulty. These include pressurized and unpressurized vehicles and external robotics that would reduce the need for extravehicular activities (EVAs), thus limiting astronaut exposure to radiation. Robotic systems are also lauded for their ability to conduct surface reconnaissance before crew arrival, scout potentially dangerous areas, and provide logistical support.
They also emphasize that future missions will require improvements in communications infrastructure since the current bandwidth is insufficient for human-rated missions. This is especially important for maintaining communications between astronauts and their families back on Earth and keeping up with the cadence of regular scientific reports. The authors advise that new satellites, antennas, the potential use of laser communications, and upgrades to the Deep Space Network (DSN) all be made.
Resources
Another priority, as predicted, involves the location and utilization of Martian resources to accomplish mission objectives. Officially known as In-Situ Resource Utilization (ISRU), this method is crucial to NASA’s plans for Lunar and Martian exploration. This includes locating sources of water ice for astronaut use but extends to the possibility of harvesting Martian regolith for base construction, all for the sake of lessening dependence on Earth. For missions sent to Mars, the opportunities for resupply will be few and far between, and it is impractical for missions to try and bring enough supplies for the full three years.
Artist’s impression of water under the Martian surface. Credit: ESA/Medialab
In any case, the authors recommend that precursor missions be tested to assess the challenges of ISRU on Mars. They acknowledge that the Artemis Program will test surface robotic and crewed infrastructure elements that will serve as pathfinders and prototypes for operations on Mars. They also point out that ISRU on the Moon has different challenges, including the fact that the Moon is an airless body, surface gravity is significantly less on the Moon (0.165 g) than on Mars (0.38 g), and temperature variations are significantly greater.
However, they stress that these tests should continue as planned, and commonalities between Lunar and Martian conditions should be identified:
“Among the most critical data sets will be orbital characterization and ground-truthing of subsurface ice deposits. Understanding the location, extent, and accessibility of these deposits will inform not only science planning but also ISRU strategies. Planetary protection Treaty obligations may require data sets demonstrating these missions would be safe for the return to Earth.”
Science Priorities
The authors of the Report stress that a cross-disciplinary consultation process is needed to ensure that scientific priorities (and the necessary tools to realize them) are set by NASA and its partners. While they acknowledge the work of the Mars Exploration Program Analysis Group (MEPAG) and the Science Objectives for Human Exploration of Mars Workshop, they state that the priorities established by both were limited in scope to engineering and robotics. Therefore, they recommended the creation of a joint effort between the Lunar Exploration Analysis Group (LEAG) and MEPAG to review these priorities.
They also recommend that these priorities reflect a multidisciplinary approach that includes human research, biological and physical science, and Lunar and Mars science. With this in mind, they made the following recommendations:
Locating water ice (vertical and horizontal extents) and taking samples to determine its composition
Accessing ice in a way that minimally impacts the samples/cores
Assessment of crew safety issues (operating on ice)
Research the effects on the human body and psyche(microgravity, transition to 1/3 G, radiation, etc.).
Robotic precursor missions to establish baseline measurements for human landing sites
HiRISE-class resolution imaging, ice mapping, and weather measurements (surface and orbit)
Robotically accessing the ice before humans arrive
Reducing the cost and increasing the cadence of robotic missions to Mars
An exploration workshop to accomplish these and other critical science objectives
The idea that Mars could have supported life at one time is the subject of ongoing debate. Image credit: NASA
Planetary Protection
Another recurring item in the Report is the issue of ensuring that human missions do not contaminate the Martian environment. This is crucial, considering that all of humanity’s astrobiological research efforts are currently focused on Mars, and crewed missions will considerably expand the search for evidence of past and present life. In particular, special care is recommended when extracting ice core samples to look for biosignatures. Therefore, the technology and methods developed must weigh the potential impact of extracting biological samples against scientific returns.
Similar recommendations are made about the possibility of humans contaminating Mars through their mere presence. “Human explorers might not be detrimental to any specific scientific investigation,” they write. “Persistent human microbial environments, such as in and around habitats, would likely change the local environmental conditions and the scope of possible science.”
Last, but not least, the authors express that care should be taken to ensure that Martian organisms are not accidentally brought back to Earth. Therefore, the Report recommends that human health and planetary protection are part of a common “critical technology challenge” that NASA should investigate ASAP. Chris Carberry, CEO and co-founder of Explore Mars and Executive Director of The Mars Society, summarized the importance of the issue:
“While participants of AMIX discussed numerous critical mission architecture, science, and human health topics, planetary protection was also included as a topic that is growing in urgency. While humans are not likely to walk on the surface of Mars until the 2030s, decisions need to be made soon regarding our planetary protection protocols. Under our current limits, human missions would not be allowed.
“However, assuming that protocols are agreed to that will allow humans to visit the surface of Mars, those protocols could impact where humans will land, what types of science will be conducted, and what access crews [will have] of in-situ resources (water, etc). All of these implications could impact overall mission architecture design and production. As such, we can’t wait unit the 2030s to agree on well-reasoned planetary protection protocols that enable a sustainable human presence on Mars.”
The Crew Transfer Vehicle (CTV) using its nuclear-thermal rocket engines to slow down and establish orbit around Mars. Credit: NASA
If there is just one takeaway from the AM IX Report, it is that there is much to be done before a crewed mission to Mars can happen. The challenges go far beyond science and engineering and extend to the well-being of astronaut crews (in the holistic sense) and far-reaching environmental considerations. It’s not enough to simply send crews to Mars and make sure they make it home in one piece. We must also ensure they can maintain contact with home, explore Mars safely and effectively, and leave the planet much as they found it (aka. the campsite rule).
According to Janet, this year’s Workshop was special because it was the first time since 2019 that all the people involved met in person:
“Coming out from what felt like a very long analog Mars mission, people were really eager to gather together and collaborate in person for the first time in three years. That seemed to really be an interesting dynamic that was quite lovely. In a way, the pandemic sort of informed some of these larger questions and the desire to find solutions. It was wonderful to know that we could meet in person and to know that even during the pandemic, the Artemis Program was still going forward, we landed another rover on the planet in 2020, and everyone came together on June 2022 with the launch of Artemis I.
“It felt more real, it felt more actionable, it’s never been more real than it is right now. I imagine there’s going to be even more excitement when we gather again this June to discuss how we build on the momentum we already have. Being able to meet face to face after three years because of the pandemic creating a kind of excitement and urgency as Mars looms ever-closer. [The prospect] of humans on Mars has gone from a theoretical possibility to a very real inevitably.”
There’s a lot to do before 2033 rolls around, and much of that work will be happening soon. Success on Mars depends heavily on the success of the Artemis Program and the validation of key technologies and strategies that will later be used to explore the Red Planet. More than that, the Artemis Program will test whether humans can operate away from Earth for extended periods. In short, it will assess whether or not humans have the capacity to become “multiplanetary.” One way or another, the next decade is going to be an exciting time!
This past week was a mixed bag for Relativity Space and their 3D-printed methane-fueled rocket engine. While the company’s Terran 1 rocket blasted off successfully on Wednesday, March 22, the second stage failed to ignite a few minutes after launch. The rocket coasted to an altitude of about 129 km and then returned to Earth, crashing a few hundred kilometers downrange.
But Relativity Space counted this first launch attempt as a success.
“Today’s launch proved Relativity’s 3D-printed rocket technologies that will enable our next vehicle, Terran R,” the company posted on Twitter. “We successfully made it through Max-Q, the highest stress state on our printed structures. This is the biggest proof point for our novel additive manufacturing approach. Today is a huge win, with many historic firsts. We also progressed through Main Engine Cutoff and Stage Separation. We will assess flight data and provide public updates over the coming days. #GoodLuckHadFun.”
Relativity’s tag line for this initial launch has been, “Good luck, have fun.”
And those who witnessed the launch were awed by the colorful plumes sent out by the rocket’s nine Aeon 1 engines as it burned the methalox fuel, seen against the night sky at Cape Canaveral Space Force Station.
“Stunning and visceral first launch, what a first to witness,” Tweeted Relativity cofounder and CEO Tim Ellis
Methalox is composed of super-chilled liquid oxygen (lox) oxidizer and liquid methane, which burns blue, green and purple. All the debris seen in the close launch images is ice, as methane ice formed on the booster, and cracked and feel off from the vibrations at lift-off.
Terran 1 stands at 33.5 meters (110-feet) tall and is designed to haul lightweight satellites into orbit. al space, lifted off from on Florida’s eastern coast at just before 11:30 pm ET. The rocket, powered by super-chilled methane and oxygen, burned a bright blue-green against the night sky.
The rocket carried a test weight made with its 3D printer, not a client satellite.
Two previous launch attempts this month were scrubbed due to issues with getting the propellant to sufficiently cold temperatures, then not enough fuel pressure, bad weather and an errant boat entering the launch zone.
Nine Aeon 1 engines power Terran 1 off the pad for its debut launch last night. Beautiful and colorful flames! pic.twitter.com/OhBXGYF5my
But even with a successful liftoff, the odds were against the rocket completing a successful mission on its first try. Back on March 7, Ellis noted on Twitter, “Of course, the rocket-loving engineer in me wants to see us be the first privately-funded AND first liquid-propellant rocket to ever reach orbit on the first try. That would be truly unprecedented.”
But the rocket did succeed at the “key inflection point” the company had set, getting the rocket through Max Q, the moment of maximum amount of pressure during flight, about 80 seconds after liftoff. — would be a “key inflection” point.
First live launch I’ve ever seen raw with my own two eyes ? I told myself when I founded @relativityspace that my first launch viewing would be our own rocket, as motivation to make it there, and here we are. What a sight to behold, feel, and hear – indescribably awe inspiring.
Relativty Space was founded in 2015 and in a first for space companies, they used massive 3D-printing machines in their Long Beach, California facility to slowly build the up the metal to form the fuselages that make up a rocket’s main body.
The company already has about $1.65 billion in launch contracts, but most of them are manifested for Relativity’s larger reusable Terran R rocket, which is still in the early stages of development. The larger medium-heavy lift Terran R rocket is expected to have the capacity to launch to orbit about 44,000 pounds (20,000 kilograms) — or 16 times more mass than what Terran 1 can lift.
Blueprint. The maiden launch of @relativityspace’s methalox powered, 3D printed Terran 1 rocket occurred last Wednesday evening at 2325 from CCSFS’ LC-16, leaving a dazzling blue trail across the skies of the eastern range. (USSF photos by Joshua Conti) pic.twitter.com/zweep6QnBK
Ellis told CNN that the company envisions using the more compact Terran 1 rocket primarily for deploying small satellites that are part of larger constellations, which can require maintenance for technology upgrades or replacement of malfunctioning satellites.
Relativity Space said on Twitter than they would be releasing more details in the coming days and weeks about what went wrong during the first launch. They have not yet announced another test flight of Terran 1.
You can watch a replay of the colorful launch, below:
Hypervelocity stars (HVS) certainly live up to their name, traveling thousands of kilometers per second or a fraction of the speed of light (relativistic speeds). These speed demons are thought to be the result of galactic or black hole mergers, globular clusters kicking out members, or binary pairs where one star is kicked out when the other goes supernova. Occasionally, these stars are fast enough to escape our galaxy and (in some cases) take their planetary systems along for the ride. This could have drastic implications for our theories of how life could be distributed throughout the cosmos (aka. panspermia theory).
There are thousands of these stars in our galaxy, and tracking them has become the task of cutting-edge astrometry missions (like the ESA’s Gaia Observatory). In previous research, astronomers suggested that these stars could be used to determine the mass of the Milky Way. In a recent study from Leiden University in the Netherlands, Ph.D. candidate Fraser Evans showed how data on HVS could be used to probe the mysteries of the most extreme objects in our Universe – supermassive black holes (SMBHs) and the violent supernovae of massive stars.
The study, titled “Far From Home: The science exploitation of the fastest milky way stars,” was conducted by Evans as part of his doctoral thesis. This consisted of using data obtained by the Gaia observatory, which has mapped over two billion stars in the Milky Way to create the largest 3D catalog of celestial objects ever made. Evans used this to conduct computer simulations where millions of stars were ejected through the Milky Way to get a better understanding of where they originate (and where their speed comes from).
To recap, all stars are traveling around the center of the Milky Way at an average velocity of 100 km/s (62 mps). What sets HVS apart is the fact that their speed is vastly greater than those of other stars, sometimes to the point where they achieve escape velocity. The existence of HVS was first predicted in 1988 by astronomer and Los Alamos National Laboratory Fellow Jack G. Hills, but the first detection was not made until 2005. Thanks to observatories like Gaia and large sky survey telescopes, astronomers have identified more than one thousand HVS since then.
Despite that, many unanswered questions exist about where HVS are most likely to originate and what mechanisms give them incredible speed. Although Evans had no particular ambition to become an astronomer as a child, his studies and research have left him fascinated by hypervelocity stars. “They’re such cool objects. A thousand kilometers per second is extremely fast. You could fly around the world in under a minute,” he said in a recent interview with the University of Leiden. “They also have a story to tell about processes in the universe about which we know little and still have much to discover.”
Most of the HVS studied so far are believed to have originated near the center of the Milky Way, where there is a larger and more tightly-bound stellar population. In addition, many of these stars are gravitationally bound by the supermassive black hole at the center of our galaxy, Sagittarius A*. But astronomers have also discovered fast-moving stars that originated in globular clusters and Magellanic Clouds, hinting that various mechanisms could be responsible. As Evans explained:
“We can assume with fairly great certainty that some of the hypervelocity stars that have now been discovered were ejected following a gravitational encounter with the massive black hole in the center of the Milky Way: Sagittarius A*. We see a similar effect in the Large Magellanic Cloud, another galaxy that we have reason to believe also contains a black hole.”
Artist’s impression of hypervelocity stars ejected from their galaxy from interaction with a black hole(far left). Credit: ESA
The possibility of a black hole within LMC was confirmed in 2021 by astronomers using the European Southern Observatory’s Very Large Telescope (VLT). This dormant black hole (VFTS 243) was found in the Tarantula Nebula, based on the motion of the stars inside of it, and was the first of its kind detected beyond the Milky Way. Based on his simulations, Evans also concluded that under the right conditions, supernovae could also eject hypervelocity stars from our galaxy. From this, Evans realized that HVS could represent an opportunity to study objects in our galaxy that are difficult to observe.
“The stars that turn into supernovae are incredibly rare in our Milky Way and the event is so short-lived that it is difficult to measure. Added to that, there are so many stars and so much dust flying around Sagittarius A* that we can’t properly see what is going on there. Some hypervelocity stars are flying in more visible parts of space and can tell us more about where they come from. For example, about the gravity of black holes or the amount of energy a supernova produces.”
In this respect, the study of HVS will build on the long history of studying black holes by observing their effects on their surrounding environment. Beyond that, they could offer insight into transient phenomena that are extremely powerful but short-lived (i.e., supernovae). Given the prodigious rate at which HVS are being detected, having a larger sample to study could mean robust scientific returns in the not-too-distant near future.
1800 light-years away, an unlikely survivor orbits an aged star. This rare planet is called a hot Neptune, and it’s one of only a small handful of hot Neptunes astronomers have found. Hot Neptunes are so close to their stars that the overpowering stellar radiation should’ve stripped away their atmospheres, leaving only a planetary core behind.
But this planet held onto its atmosphere somehow.
The more exoplanets we find, the better we understand the exoplanet population. With over 5,300 confirmed exoplanets, scientists are getting a handle on the makeup of the exoplanet population. On their Exoplanet Discovery Dashboard, NASA groups exoplanets into these categories: Neptune-like, Gas Giant, Super-Earth, and Terrestrial. Other classifications are used in space science, too, like hot Jupiter. But the hot Neptune tag isn’t used much because there aren’t many of them.
A hot Neptune is a gaseous planet that is extremely close to its star, just as a hot Jupiter is. When a gas planet gets too close to its star, the star can strip the gaseous atmosphere away. Hot Jupiters are so massive that they can hang on to their atmospheres with some success. But Neptune-size planets are much less massive than Jupiter-size planets, and really, hot Neptunes just shouldn’t exist. They’re not massive enough to hold onto their atmospheres in the face of all the stellar radiation. They defy the odds.
“The discovery of a low-density hot Neptune orbiting an evolved star demonstrates that the atmospheres of these planets are more resilient than previously thought.”
From “
The first hot Neptune astronomers found is Gliese 436 b. Astronomers found it in 2004, five years before the Kepler mission changed exoplanet science forever. Researchers are still puzzling over Gliese 436 b and trying to understand how it held onto its atmosphere for this long. A 2015 paper concluded that the planet is losing mass and leaving a trail of hydrogen behind it as the star strips away its atmosphere.
Artist’s impression of JG436b, a hot Neptune located about 33 light years from Earth. The planet is still a puzzle, as are all hot Neptunes. Credit: Courtesy Space Telescope Science Institute
In new research, astronomers from the USA and Australia presented their discovery of another hot Neptune. The paper is “An unlikely survivor: a low-density hot Neptune orbiting a red giant star.” The lead author is Samuel Grunblatt from the Department of Physics and Astronomy at Johns Hopkins University.
This hot Neptune is so close to its star that it completes an orbit in only 4.2 days. The planet, named TIC 365102760 b, is not very dense. Even though it’s about half the radius of Jupiter, its density is only 0.06 that of Jupiter’s. With a density that low, the planet shouldn’t be hanging onto its atmosphere.
The star is ancient, a red giant about 7.2 billion years old, and is 1.2 times as massive as the Sun. Its temperature is 4700 Kelvin (4400 C; 8,000 F.) Considering all these factors, TIC 365102760 b should be nothing but a planetary core by now. “The old age and high equilibrium temperature yet remarkably low density of this planet suggests that its gaseous envelope should have been stripped by high-energy stellar irradiation billions of years ago,” the authors write.
This planet is the rarest of the rare. There is only a small handful of Neptune-size planets orbiting a post-main sequence star, and it’s the only hot Neptune orbiting this type of star. Outliers like these are important because they can define Nature’s limits and help scientists build better models.
Current models can’t explain TIC 365102760 b and instead show that there should be nothing left by now but a core. “Thus, assuming that the planet did not experience migration or inflation after a system age of 20 Myr, most or all of the planet’s atmosphere should have been stripped over its lifetime,” the authors write.
How was it able to hold onto its mass for so long while being so close to its star?
Atmospheric stripping is a well-known phenomenon. If a planet is too close to its star, or if it lacks a protective magnetic shield, powerful radiation can strip the planet’s atmosphere away. This artist’s rendering shows a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere. Credits: NASA/GSFC
The authors say that the explanation could lie in incorrect models of stellar flux. If the star isn’t as powerful as thought, then that could explain how the planet has held onto its atmosphere for so long. “First, the stellar flux in XUV may be significantly lower or absorbed less efficiently than existing models predict, preventing severe atmospheric erosion even if the planet has not changed its orbit or radius since formation.”
Migration could explain the planet, too, but only if it migrated during the star’s main sequence lifetime. “Second, the planet may have migrated to its current orbit during the main sequence lifetime of its host star from a previous larger orbit, avoiding the highest intensity of XUV irradiation from its host star,” they explain.
But there are some problems with that explanation. Star-planet and planet-planet interactions could’ve caused the migration, but there’s no indication of another large planet relatively near TIC 365102760 b. Interactions between a planet and a star can trigger migration, but in those cases, the planet has a highly-eccentric orbit. “Furthermore, TIC 365102760 b does not appear to have a high-eccentricity orbit, suggesting that migration due to star-planet interaction is also unlikely or not very recent in the system’s history,” the authors write.
The researchers suggest a third possibility to explain the hot Neptune. It could’ve been significantly smaller in the past, “… limiting the instantaneous rate of mass loss on the main sequence.” Planets are known to inflate as their stars leave the main sequence due to an increase in received radiation. But at this level of detail, much of the potential explanation comes down to different models, and there’s simply not enough clarity to attach any certainty to the explanation.
Gaseous planets are known to inflate when their stars leave the main sequence and irradiate their planets more powerfully. This illustration shows the exoplanet K2-132b. The upper left shows the planet during the star’s main sequence lifetime, and the lower left panel shows how the planet expanded when the star left the main sequence. Image Credit: Karen Teramura, University of Hawaii Institute for Astronomy.
The researchers are shying away from the late-stage migration explanation. “Current observational evidence for both late-stage inflation and/or weak photoevaporation is stronger than evidence for late-stage migration in this system,” they explain. They think that a weaker level of XUV radiation from the star alongside late-stage inflation is the best explanation for this hot Neptune’s persistence.
But even without a clear explanation for TIC 365102760 b’s resilience, the planet and this research are telling planetary scientists some important things.
“The discovery of a low-density hot Neptune orbiting an evolved star demonstrates that the atmospheres of these planets are more resilient than previously thought,” the authors write. The planet’s existence also shows that planets smaller than Jupiter can become inflated as their stars evolve out of the main sequence. This has implications for our understanding of how Neptune-size planets form and evolve and implications for how scientists interpret the exoplanet population.
This figure from the research shows the planetary radius on the y-axis and atmospheric loss divided by the planetary mass on the x-axis. TIC 365102760 b is denoted by the star symbol. The exoplanet’s atmospheric mass is predicted to be smaller than the total mass expected to have been lost. It’s a puzzle how the planet has retained an atmosphere given its radius and orbit near its star. Image Credit: Grunblatt et al. 2023.
Since the star and planet are so closely intertwined, these results can tell us something about planet composition and stellar activity, too. But that still needs to be untangled. Finding more of these rare planets is the obvious path forward, but they don’t often appear in general searches. “Focused searches for these evolved systems are necessary as these planets are missed by general searches for transiting planets,” the authors write.
As for TIC 365102760 b’s specific case, follow-up observations could more tightly constrain the planet’s characteristics and help explain its existence. Ground-based and space-based spectroscopic studies could reveal atmospheric outflows from the planet more clearly and could shed light on the lifetime of its atmosphere as well as the atmosphere’s composition.
“Constraining the balance between planet atmospheric inflation and mass loss will help reveal the evolution of planetary atmospheres over time, clarifying planet demographic features such as the hot Neptune desert,” the authors conclude.
There’s a reason Jezero Crater was chosen as the landing site for the Perseverance Rover: it is considered one of the likeliest places to find any evidence if Mars was ever habitable for long periods of time. In this great new flyby video from ESA, you can get a birds-eye look at Perseverance’s home.
Created from data ESA’s Mars Express and NASA’s Mars Reconnaissance Orbiter, the video takes you on an aerial tour of the crater. From this perspective, you can see the water features in this ancient impact crater and understand why this was considered one of the best places to explore Mars.
Perseverance landed in Jezero crater in February 2021. The diverse rocks and mineralogy found in and around Jezero crater tell the story of Mars’ complex geological history, which Perseverance is working to study and reveal. The roughly 45-km-wide crater is found on the border between the ancient region of Terra Sabaea – which contains rocks of up to 4.1 billion years old – and the younger Isidis Planitia basin, which formed via asteroid impact.
Did the crater ever host water? The evidence so far suggests the wall of Jezero is breached by three valleys that were once rivers of flowing water, and the crater is considered to be an ancient ‘open basin lake’ in that water once flowed both into and out of the crater, a type of basin that is especially promising in the hunt for life on Mars.
A screenshot from an interactive map that shows the landing site and path traveled so far (March 2023) for NASA’s Perseverance rover within Jezero Crater. Perseverance landed on Feb. 18, 2021. You can see the map online here.
In the video, you’ll see an outflow channel snaking away from the crater wall and towards the camera perspective. Then you’ll see two inflow channels (Neretva Vallis and Sava Vallis, found on the western-northwestern rim of Jezero. the most prominent of these branches out into the crater to form an ancient fan-shaped river delta that was the landing site for Perseverance.
Or are these features created by ancient volcanism? Jezero sits next to an intriguing system of faults known as Nili Fossae and a prominent area of volcanism named Syrtis Major, where lava flowed some three billion years ago.
To really know for sure, scientists will need to study Mars close up. To that end, Perseverance is collecting samples of Martian rock and soil and putting them in special containers that will one day be picked up by a future sample return mission. NASA and ESA are working together on this mission, which ESA says will be more advanced than any robotic missions that have gone before, but it will revolutionize our understanding of both the Red Planet and the Solar System.
