NASA: Some Icy Exoplanets May Have Habitable Oceans and Geysers

A NASA study expands the search for life beyond our solar system by indicating that 17 exoplanets (worlds outside our solar system) could have oceans of liquid water, an essential ingredient for life, beneath icy shells. Water from these oceans could occasionally erupt through the ice crust as geysers. The science team calculated the amount of geyser activity on these exoplanets, the first time these estimates have been made. They identified two exoplanets sufficiently close where signs of these eruptions could be observed with telescopes.

The search for life elsewhere in the Universe typically focuses on exoplanets that are in a star’s “habitable zone,” a distance where temperatures allow liquid water to persist on their surfaces. However, it’s possible for an exoplanet that’s too distant and cold to still have an ocean underneath an ice crust if it has enough internal heating. Such is the case in our solar system where Europa, a moon of Jupiter, and Enceladus, a moon of Saturn, have subsurface oceans because they are heated by tides from the gravitational pull of the host planet and neighboring moons.

These subsurface oceans could harbor life if they have other necessities, such as an energy supply as well as elements and compounds used in biological molecules. On Earth, entire ecosystems thrive in complete darkness at the bottom of oceans near hydrothermal vents, which provide energy and nutrients.

“Our analyses predict that these 17 worlds may have ice-covered surfaces but receive enough internal heating from the decay of radioactive elements and tidal forces from their host stars to maintain internal oceans,” said Dr. Lynnae Quick of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Thanks to the amount of internal heating they experience, all planets in our study could also exhibit cryovolcanic eruptions in the form of geyser-like plumes.” Quick is lead author of a paper on the research published on October 4 in the Astrophysical Journal.

The team considered conditions on 17 confirmed exoplanets that are roughly Earth-sized but less dense, suggesting that they could have substantial amounts of ice and water instead of denser rock. Although the planets’ exact compositions remain unknown, initial estimates of their surface temperatures from previous studies all indicate that they are much colder than Earth, suggesting that their surfaces could be covered in ice.

The study improved estimates of each exoplanet’s surface temperature by recalculating using the known surface brightness and other properties of Europa and Enceladus as models. The team also estimated the total internal heating in these exoplanets by using the shape of each exoplanet’s orbit to get the heat generated from tides and adding it to the heat expected from radioactive activity. Surface temperature and total heating estimates gave the ice layer thickness for each exoplanet since the oceans cool and freeze at the surface while being heated from the interior. Finally, they compared these figures to Europa’s and used estimated levels of geyser activity on Europa as a conservative baseline to estimate geyser activity on the exoplanets.

They predict that surface temperatures are colder than previous estimates by up to 60 degrees Fahrenheit (16 degrees Celsius). Estimated ice shell thickness ranged from about 190 feet (58 meters) for Proxima Centauri b and one mile (1.6 kilometers) for LHS 1140 b to 24 miles (38.6 kilometers) for MOA 2007 BLG 192Lb, compared to Europa’s estimated average of 18 miles (almost 29 kilometers). Estimated geyser activity went from just 17.6 pounds per second (about 8 kilograms/second) for Kepler 441b to 639,640 pounds/second (290,000 kilograms/second) for LHS 1140 b and 13.2 million pounds/second (six million kilograms/second) for Proxima Centauri b, compared to Europa at 4,400 pounds/second (2,000 kilograms/second).

“Since our models predict that oceans could be found relatively close to the surfaces of Proxima Centauri b and LHS 1140 b, and their rate of geyser activity could exceed Europa’s by hundreds to thousands of times, telescopes are most likely to detect geological activity on these planets,” said Quick, who is presenting this research December 12 at the American Geophysical Union meeting in San Francisco, California.

This activity could be seen when the exoplanet passes in front of its star. Certain colors of starlight could be dimmed or blocked by water vapor from the geysers. “Sporadic detections of water vapor in which the amount of water vapor detected varies with time, would suggest the presence of cryovolcanic eruptions,” said Quick. The water might contain other elements and compounds that could reveal if it can support life. Since elements and compounds absorb light at specific “signature” colors, analysis of the starlight would let scientists determine the geyser’s composition and evaluate the exoplanet’s habitability potential.

For planets like Proxima Centauri b that don’t cross their stars from our vantage point, geyser activity could be detected by powerful telescopes that are able to measure light that the exoplanet reflects while orbiting its star. Geysers would expel icy particles at the exoplanet’s surface which would cause the exoplanet to appear very bright and reflective.

The research was funded by NASA’s Habitable Worlds Program, the University of Washington’s Astrobiology Program, and the Virtual Planetary Laboratory, a member of the NASA Nexus for Exoplanet System Science coordination group.

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NASA’s Perseverance Rover Deciphers Ancient History of Martian Lake

Now at 1,000 days on Mars, the mission has traversed an ancient river and lake system, collecting valuable samples along the way.

Marking its 1,000th Martian day on the Red Planet, NASA’s Perseverance rover recently completed its exploration of the ancient river delta that holds evidence of a lake that filled Jezero Crater billions of years ago. The six-wheeled scientist has to date collected a total of 23 samples, revealing the geologic history of this region of Mars in the process.

One sample called “Lefroy Bay” contains a large quantity of fine-grained silica, a material known to preserve ancient fossils on Earth. Another, “Otis Peak,” holds a significant amount of phosphate, which is often associated with life as we know it. Both of these samples are also rich in carbonate, which can preserve a record of the environmental conditions from when the rock was formed.

The discoveries were shared Tuesday, Dec. 12, at the American Geophysical Union fall meeting in San Francisco.

“We picked Jezero Crater as a landing site because orbital imagery showed a delta – clear evidence that a large lake once filled the crater. A lake is a potentially habitable environment, and delta rocks are a great environment for entombing signs of ancient life as fossils in the geologic record,” said Perseverance’s project scientist, Ken Farley of Caltech. “After thorough exploration, we’ve pieced together the crater’s geologic history, charting its lake and river phase from beginning to end.”

Jezero formed from an asteroid impact almost 4 billion years ago. After Perseverance landed in February 2021, the mission team discovered the crater floor is made of igneous rock formed from magma underground or from volcanic activity at the surface. They have since found sandstone and mudstone, signaling the arrival of the first river in the crater hundreds of millions of years later. Above these rocks are salt-rich mudstones, signaling the presence of a shallow lake experiencing evaporation. The team thinks the lake eventually grew as wide as 22 miles (35 kilometers) in diameter and as deep as 100 feet (30 meters).

Later, fast-flowing water carried in boulders from outside Jezero, distributing them atop of the delta and elsewhere in the crater.

“We were able to see a broad outline of these chapters in Jezero’s history in orbital images, but it required getting up close with Perseverance to really understand the timeline in detail,” said Libby Ives, a postdoctoral fellow at NASA’s Jet Propulsion Laboratory in Southern California, which manages the mission.

Enticing Samples

The samples Perseverance gathers are about as big as a piece of classroom chalk and are stored in special metal tubes as part of the Mars Sample Return campaign, a joint effort by NASA and ESA (European Space Agency). Bringing the tubes to Earth would enable scientists to study the samples with powerful lab equipment too large to take to Mars.

To decide which samples to collect, Perseverance first uses an abrasion tool to wear away a patch of a prospective rock and then studies the rock’s chemistry using precision science instruments, including the JPL-built Planetary Instrument for X-ray Lithochemistry, or PIXL.

At a target the team calls “Bills Bay,” PIXL spotted carbonates – minerals that form in watery environments with conditions that might be favorable for preserving organic molecules. (Organic molecules form by both geological and biological processes.) These rocks were also abundant with silica, a material that’s excellent at preserving organic molecules, including those related to life.

“On Earth, this fine-grained silica is what you often find in a location that was once sandy,” said JPL’s Morgan Cable, the deputy principal investigator of PIXL. “It’s the kind of environment where, on Earth, the remains of ancient life could be preserved and found later.”

Perseverance’s instruments are capable of detecting both microscopic, fossil-like structures and chemical changes that may have been left by ancient microbes, but they have yet to see evidence for either.

At another target PIXL examined, called “Ouzel Falls,” the instrument detected the presence of iron associated with phosphate. Phosphate is a component of DNA and the cell membranes of all known terrestrial life and is part of a molecule that helps cells carry energy.

After assessing PIXL’s findings on each of these abrasion patches, the team sent up commands for the rover to collect rock cores close by: Lefroy Bay was collected next to Bills Bay, and Otis Peak at Ouzel Falls.

“We have ideal conditions for finding signs of ancient life where we find carbonates and phosphates, which point to a watery, habitable environment, as well as silica, which is great at preservation,” Cable said.

Perseverance’s work is, of course, far from done. The mission’s ongoing fourth science campaign will explore Jezero Crater’s margin, near the canyon entrance where a river once flooded the crater floor. Rich carbonate deposits have been spotted along the margin, which stands out in orbital images like a ring within a bathtub.

More About the Mission

A key objective for Perseverance’s mission on Mars is astrobiology, including the search for signs of ancient microbial life. The rover will characterize the planet’s geology and past climate, pave the way for human exploration of the Red Planet, and be the first mission to collect and cache Martian rock and regolith (broken rock and dust).

Subsequent NASA missions, in cooperation with ESA (European Space Agency), would send spacecraft to Mars to collect these sealed samples from the surface and return them to Earth for in-depth analysis.

The Mars 2020 Perseverance mission is part of NASA’s Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet.

JPL, which is managed for NASA by Caltech in Pasadena, California, built and manages operations of the Perseverance rover.

For more about Perseverance:

mars.nasa.gov/mars2020/

News Media Contacts

Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-2433
andrew.c.good@jpl.nasa.gov

Karen Fox / Alana Johnson
NASA Headquarters, Washington
301-286-6284 / 202-358-1501
karen.c.fox@nasa.gov / alana.r.johnson@nasa.gov

2023-181

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Webb Sheds Light on an Exploded Star

Supernova remnant Cassiopeia A (Cas A) shines in a new image from Dec. 10, 2023, from NASA’s James Webb Space Telescope. Webb’s Near-Infrared Camera (NIRCam) view of Cas A displays this stellar explosion at a resolution previously unreachable at these wavelengths, revealing intricate details of the expanding shell of material slamming into the gas shed by the star before it exploded.

Cas A is one of the most well-studied supernova remnants in all the cosmos. Over the years, ground-based and space-based observatories, including NASA’s Chandra X-Ray Observatory, Hubble Space Telescope, and retired Spitzer Space Telescope have assembled a multiwavelength picture of the object’s remnant.

However, astronomers have now entered a new era in the study of Cas A. In April 2023, Webb’s Mid-Infrared Instrument (MIRI) started this chapter, unveiling new and unexpected features within the inner shell of the supernova remnant. Many of those features are invisible in the new NIRCam image, and astronomers are investigating why.

Read on to find out what we can learn from this new image of Cassiopeia A.

Image Credit: NASA, ESA, CSA, STScI, D. Milisavljevic (Purdue University), T. Temim (Princeton University), I. De Looze (University of Gent)

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