Juno’s first image of Europa released

Newswand: Jupiter’s moon Europa’s picture, being taken by NASA’s Juno spacecraft for the first time, has been released by NASA after the spacecraft performed a close flyby on September 29.

Photo credit: NASA/JPL-Caltech/SWRI/MSSS

Revealing surface features in a region near the moon’s equator called Annwn Regio, the image was captured during the solar-powered spacecraft’s closest approach, on Thursday, Sept. 29, at 2:36 a.m. PDT (5:36 a.m. EDT), at a distance of about 219 miles (352 kilometers).

This is only the third close pass in history below 310 miles (500 kilometers) altitude and the closest look any spacecraft has provided at Europa since Jan. 3, 2000, when NASA’s Galileo came within 218 miles (351 kilometers) of the surface.

Europa is the sixth-largest moon in the solar system, slightly smaller than Earth’s moon. Scientists think a salty ocean lies below a miles-thick ice shell, sparking questions about potential conditions capable of supporting life underneath Europa’s surface.

This segment of the first image of Europa taken during this flyby by the spacecraft’s JunoCam (a public-engagement camera) zooms in on a swath of Europa’s surface north of the equator. Due to the enhanced contrast between light and shadow seen along the terminator (the night side boundary), rugged terrain features are easily seen, including tall shadow-casting blocks, while bright and dark ridges and troughs curve across the surface. The oblong pit near the terminator might be a degraded impact crater.

With this additional data about Europa’s geology, Juno’s observations will benefit future missions to the Jovian moon, including the agency’s Europa Clipper. Set to launch in 2024, Europa Clipper will study the moon’s atmosphere, surface, and interior, with its main science goal being to determine whether there are places below Europa’s surface that could support life.

As exciting as Juno’s data will be, the spacecraft had only a two-hour window to collect it, racing past the moon with a relative velocity of about 14.7 miles per second (23.6 kilometers per second).

“It’s very early in the process, but by all indications Juno’s flyby of Europa was a great success,” said Scott Bolton, Juno principal investigator from Southwest Research Institute in San Antonio. “This first picture is just a glimpse of the remarkable new science to come from Juno’s entire suite of instruments and sensors that acquired data as we skimmed over the moon’s icy crust.”

During the flyby, the mission collected what will be some of the highest-resolution images of the moon (0.6 miles, or 1 kilometer, per pixel) and obtained valuable data on Europa’s ice shell structure, interior, surface composition, and ionosphere, in addition to the moon’s interaction with Jupiter’s magnetosphere.

“The science team will be comparing the full set of images obtained by Juno with images from previous missions, looking to see if Europa’s surface features have changed over the past two decades,” said Candy Hansen, a Juno co-investigator who leads planning for the camera at the Planetary Science Institute in Tucson, Arizona. “The JunoCam images will fill in the current geologic map, replacing existing low-resolution coverage of the area.”

Juno’s close-up views and data from its Microwave Radiometer (MWR) instrument will provide new details on how the structure of Europa’s ice varies beneath its crust. Scientists can use all this information to generate new insights into the moon, including data in the search for regions where liquid water may exist in shallow subsurface pockets.

Building on Juno’s observations and previous missions such as Voyager 2 and Galileo, NASA’s Europa Clipper mission, slated to arrive at Europa in 2030, will study the moon’s atmosphere, surface, and interior – with a goal to investigate habitability and better understand its global subsurface ocean, the thickness of its ice crust, and search for possible plumes that may be venting subsurface water into space.

The close flyby modified Juno’s trajectory, reducing the time it takes to orbit Jupiter from 43 to 38 days. The flyby also marks the second encounter with a Galilean moon during Juno’s extended mission. The mission explored Ganymede in June 2021 and is scheduled to make close flybys of Io, the most volcanic body in the solar system, in 2023 and 2024.

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Two Super-Mercuries found

Newswand: Researchers at Instituto de Astrofísica e Ciências do Espaço have found two Super-Mercuries in the star system of HD 23472 and trying to find out the reason for the formation of such planets.

Photo credit: NASA/JPL-Caltech

While observing the star system HD 23472 with the ESPRESSO1 spectrograph (ESO), a team led by Instituto de Astrofísica e Ciências do Espaço’s (IA3) researcher Susana Barros (IA & Dep. de Física e Astronomia – Faculdade de Ciências da Universidade do Porto), found three super-earths and two Super-Mercuries. This last type of exoplanet is still very rare – counting these two, there are only eight known Super-Mercuries.

The objective of the study, published in the journal Astronomy & Astrophysics, was to characterize the composition of small planets and understand how it changes with the planet’s position, temperature and the stellar properties. Susana Barros explains that the team aimed to: “study the transition between having or not having an atmosphere, which could be related to the evaporation of the atmosphere due to the irradiation of the star.”

“The team found that this system is composed of three super-Earths with a significant atmosphere and surprisingly two Super-Mercuries, which are the closest planets to the star.” concludes Susana Barros.

Of the five planets in the HD 23472 system, three have masses smaller than the Earth. These are among the lightest exoplanets whose masses were measured using the radial velocity method, which was only possible due to the very high precision of ESPRESSO, installed in ESO’s Very Large Telescope (VLT), in Chile.  And the presence of not one, but two super-Mercuries, left the team wanting to go further.

The planet Mercury, in the Solar System, has a relatively larger core and relatively smaller mantle than the other planets, but we don’t know why. Some possible explanations involve a giant impact which removed part of the planet’s mantle or, because of its high temperature, part of Mercury’s mantle could have evaporated. Surprisingly, other exoplanets with similar characteristics, called Super-Mercuries, were recently found around other stars.

Barros adds: “For the first time we have discovered a system with two Super-Mercuries. This allows us to obtain clues about how these planets were formed, which could help us exclude some possibilities. For example, if an impact large enough to create a Super-Mercury is already very unlikely, two giant impacts in the same system seems very improbable. We still don’t know how these planets are formed but it appears to be connected to the composition of the parent star. This new system can help us find out”.

Member of the team Olivier Demangeon (IA & DFA-FCUP), comments : “Understanding how these two Super-Mercuries have formed will require further characterization of the composition of these planets. As these planets have radii smaller than the Earth, current instrumentation does not have the sensitivity to probe the composition of their surface, or the existence and composition of a potential atmosphere. The future Extremely Large Telescope (ELT) and its first generation high resolution spectrograph ANDES, will for the first time provide both the required sensitivity and precision to attempt such observations.”

But the ultimate goal is to find other Earth’s. “The existence of the atmosphere gives us insight into the formation and evolution of the system and also has implications on the habitability of planets. I would like to extend this type of study to longer period planets which have more amenable temperatures”, says Barros.

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NASA’s DART Mission hits asteroid in first-ever planetary defense test

Newswand: NASA’s Double Asteroid Redirection Test (DART) – the world’s first planetary defense technology demonstration – successfully impacted its asteroid target on Monday, after 10 months flying in space.

Photo credit: NASA

Mission control at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, announced the successful impact at 7:14 p.m. EDT.

As a part of NASA’s overall planetary defense strategy, DART’s impact with the asteroid Dimorphos demonstrates a viable mitigation technique for protecting the planet from an Earth-bound asteroid or comet, if one were discovered.

“At its core, DART represents an unprecedented success for planetary defense, but it is also a mission of unity with a real benefit for all humanity,” said NASA Administrator Bill Nelson. “As NASA studies the cosmos and our home planet, we’re also working to protect that home, and this international collaboration turned science fiction into science fact, demonstrating one way to protect Earth.”

DART targeted the asteroid moonlet Dimorphos, a small body just 530 feet (160 meters) in diameter. It orbits a larger, 2,560-foot (780-meter) asteroid called Didymos. Neither asteroid poses a threat to Earth.

The mission’s one-way trip confirmed NASA can successfully navigate a spacecraft to intentionally collide with an asteroid to deflect it, a technique known as kinetic impact.

The investigation team will now observe Dimorphos using ground-based telescopes to confirm that DART’s impact altered the asteroid’s orbit around Didymos. Researchers expect the impact to shorten Dimorphos’ orbit by about 1%, or roughly 10 minutes; precisely measuring how much the asteroid was deflected is one of the primary purposes of the full-scale test.

“Planetary Defense is a globally unifying effort that affects everyone living on Earth,” said Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. “Now we know we can aim a spacecraft with the precision needed to impact even a small body in space. Just a small change in its speed is all we need to make a significant difference in the path an asteroid travels.”

The spacecraft’s sole instrument, the Didymos Reconnaissance and Asteroid Camera for Optical navigation (DRACO), together with a sophisticated guidance, navigation and control system that works in tandem with Small-body Maneuvering Autonomous Real Time Navigation (SMART Nav) algorithms, enabled DART to identify and distinguish between the two asteroids, targeting the smaller body.

These systems guided the 1,260-pound (570-kilogram) box-shaped spacecraft through the final 56,000 miles (90,000 kilometers) of space into Dimorphos, intentionally crashing into it at roughly 14,000 miles (22,530 kilometers) per hour to slightly slow the asteroid’s orbital speed. DRACO’s final images, obtained by the spacecraft seconds before impact, revealed the surface of Dimorphos in close-up detail.

Fifteen days before impact, DART’s CubeSat companion Light Italian CubeSat for Imaging of Asteroids (LICIACube), provided by the Italian Space Agency, deployed from the spacecraft to capture images of DART’s impact and of the asteroid’s resulting cloud of ejected matter. In tandem with the images returned by DRACO, LICIACube’s images are intended to provide a view of the collision’s effects to help researchers better characterize the effectiveness of kinetic impact in deflecting an asteroid. Because LICIACube doesn’t carry a large antenna, images will be downlinked to Earth one by one in the coming weeks.

“DART’s success provides a significant addition to the essential toolbox we must have to protect Earth from a devastating impact by an asteroid,” said Lindley Johnson, NASA’s Planetary Defense Officer. “This demonstrates we are no longer powerless to prevent this type of natural disaster. Coupled with enhanced capabilities to accelerate finding the remaining hazardous asteroid population by our next Planetary Defense mission, the Near-Earth Object (NEO) Surveyor, a DART successor could provide what we need to save the day.”

With the asteroid pair within 7 million miles (11 million kilometers) of Earth, a global team is using dozens of telescopes stationed around the world and in space to observe the asteroid system. Over the coming weeks, they will characterize the ejecta produced and precisely measure Dimorphos’ orbital change to determine how effectively DART deflected the asteroid. The results will help validate and improve scientific computer models critical to predicting the effectiveness of this technique as a reliable method for asteroid deflection.

“This first-of-its-kind mission required incredible preparation and precision, and the team exceeded expectations on all counts,” said APL Director Ralph Semmel. “Beyond the truly exciting success of the technology demonstration, capabilities based on DART could one day be used to change the course of an asteroid to protect our planet and preserve life on Earth as we know it.”

Roughly four years from now, the European Space Agency’s Hera project will conduct detailed surveys of both Dimorphos and Didymos, with a particular focus on the crater left by DART’s collision and a precise measurement of Dimorphos’ mass.

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Heat wave of 700 degrees Celsius observed on Jupiter

Newswand: An unexpected ‘heat wave’ of 700 degrees Celsius, extending 130,000 kilo metres (10 Earth diameters) in Jupiter’s atmosphere, has been discovered. James O’Donoghue, of the Japanese Aerospace Exploration Agency (JAXA), has presented the results this week at the Europlanet Science Congress (EPSC) 2022 in Granada. 

Photo credit: Euro Planet Society

Jupiter’s atmosphere, famous for its characteristic multi colored vortices, is also unexpectedly hot: in fact, it is hundreds of degrees hotter than models predict. Due to its orbital distance millions of kilo metres from the Sun, the giant planet receives under 4% of the amount of sunlight compared to Earth, and its upper atmosphere should theoretically be a frigid -70 degrees Celsius. Instead, its cloud tops are measured everywhere at over 400 degrees Celsius.

“Last year we produced – and presented at EPSC2021 – the first maps of Jupiter’s upper atmosphere capable of identifying the dominant heat sources,” said Dr O’Donoghue. “Thanks to these maps, we demonstrated that Jupiter’s auroras were a possible mechanism that could explain these temperatures.”

Just like the Earth, Jupiter experiences auroras around its poles as an effect of the solar wind. However, while Earth’s auroras are transient and only occur when solar activity is intense, auroras at Jupiter are permanent and have a variable intensity. The powerful auroras can heat the region around the poles to over 700 degrees Celsius, and global winds can redistribute the heat globally around Jupiter.

Looking more deeply through their data, Dr O’Donoghue and his team discovered the spectacular ‘heat wave’ just below the northern aurora, and found that it was travelling towards the equator at a speed of thousands of kilo metres per hour.

The heat wave was probably triggered by a pulse of enhanced solar wind plasma impacting Jupiter’s magnetic field, which boosted auroral heating and forced hot gases to expand and spill out towards the equator.

“While the auroras continuously deliver heat to the rest of the planet, these heat wave ‘events’ represent an additional, significant energy source,” added Dr O’Donoghue. “These findings add to our knowledge of Jupiter’s upper-atmospheric weather and climate, and are a great help in trying to solve the ‘energy crisis’ problem that plagues research into the giant planets.”

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Juno spacecraft to perform close flyby of Europa on 29

Newswand: NASA’s Juno spacecraft would perform a close flyby of Jupiter’s moon, Europa on September 29 to take a close look at the ice covered moon of Jupiter.

On Thursday, Sept. 29, at 2:36 a.m. PDT (5:36 a.m. EDT), NASA’s Juno spacecraft will come within 222 miles (358 kilometers) of the surface of Europa. The solar-powered spacecraft is expected to obtain some of the highest-resolution images ever taken of portions of Europa’s surface, as well as collect valuable data on the moon’s interior, surface composition, and ionosphere, along with its interaction with Jupiter’s magnetosphere.

Such information could benefit future missions, including the agency’s Europa Clipper, which is set to launch in 2024 to study the icy moon. “Europa is such an intriguing Jovian moon, it is the focus of its own future NASA mission,” said Juno Principal Investigator Scott Bolton of the Southwest Research Institute in San Antonio. “We’re happy to provide data that may help the Europa Clipper team with mission planning, as well as provide new scientific insights into this icy world.”

With an equatorial diameter of 1,940 miles (3,100 kilometers), Europa is about 90% the size of Earth’s Moon. Scientists think a salty ocean lies below a miles-thick ice shell, sparking questions about potential conditions capable of supporting life underneath Europa’s surface.

The close flyby will modify Juno’s trajectory, reducing the time it takes to orbit Jupiter from 43 to 38 days. It will be the closest a NASA spacecraft has approached Europa since Galileo came within 218 miles (351 kilometers) on Jan. 3, 2000. In addition, this flyby marks the second encounter with a Galilean moon during Juno’s extended mission. The mission explored Ganymede in June 2021 and plans to make close approaches of Io in 2023 and 2024.

Data collection will begin an hour prior to closest approach, when the spacecraft is 51,820 miles (83,397 kilometers) from Europa.

“The relative velocity between spacecraft and moon will be 14.7 miles per second (23.6 kilometers per second), so we are screaming by pretty fast,” said John Bordi, Juno deputy mission manager at JPL. “All steps have to go like clockwork to successfully acquire our planned data, because soon after the flyby is complete, the spacecraft needs to be reoriented for our upcoming close approach of Jupiter, which happens only 7 ½ hours later.”

The spacecraft’s full suite of instruments and sensors will be activated for the Europa encounter. Juno’s Jupiter Energetic-Particle Detector Instrument (JEDI) and its medium-gain (X-band) radio antenna will collect data on Europa’s ionosphere. Its Waves, Jovian Auroral Distributions Experiment (JADE), and Magnetometer (MAG) experiments will measure plasma in the moon’s wake as Juno explores Europa’s interaction with Jupiter’s magnetosphere.

MAG and Waves will also search for possible water plumes above Europa’s surface. “We have the right equipment to do the job, but to capture a plume will require a lot of luck,” said Bolton. “We have to be at the right place at just the right time, but if we are so fortunate, it’s a home run for sure.”

Inside and out

Juno’s Microwave Radiometer (MWR) will peer into Europa’s water-ice crust, obtaining data on its composition and temperature. This is the first time such data will have been collected to study the moon’s icy shell.

In addition, the mission expects to take four visible-light images of the moon with JunoCam (a public-engagement camera) during the flyby. The Juno science team will compare them to images from previous missions, looking for changes in Europa’s surface features that might have occurred over the past two decades. These visible-light images will have an expected resolution better than 0.6 miles (1 kilometer) per pixel.

Although Juno will be in Europa’s shadow when closest to the moon, Jupiter’s atmosphere will reflect enough sunlight for Juno’s visible-light imagers to collect data. Designed to take images of star fields and search for bright stars with known positions to help Juno get its bearings, the mission’s star camera (called the Stellar Reference Unit) will take a high-resolution black-and-white image of Europa’s surface. Meanwhile, the Jovian Infrared Auroral Mapper (JIRAM) will attempt to collect infrared images of its surface.

Juno’s closeup views and data from its MWR instrument will inform the Europa Clipper mission, which will perform nearly 50 flybys after it arrives at Europa in 2030. Europa Clipper will gather data on the moon’s atmosphere, surface, and interior – information that scientists will use to better understand Europa’s global subsurface ocean, the thickness of its ice crust, and possible plumes that may be venting subsurface water into space.

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Webb captures clearest picture of rings of Neptune

Newswand: NASA’s James Webb Space Telescope has captured the clear picture of rings of Neptune and has shown the planet in whole new light. It has shown off its capabilities closer to home with its first image of Neptune. Not only has Webb captured the clearest view of this distant planet’s rings in more than 30 years, but its cameras reveal the ice giant in a whole new light.

Photo credit: NASA, ESA, CSA, STScI

Most striking in Webb’s new image is the crisp view of the planet’s rings – some of which have not been detected since NASA’s Voyager 2 became the first spacecraft to observe Neptune during its flyby in 1989. In addition to several bright, narrow rings, the Webb image clearly shows Neptune’s fainter dust bands.

“It has been three decades since we last saw these faint, dusty rings, and this is the first time we’ve seen them in the infrared,” notes Heidi Hammel, a Neptune system expert and interdisciplinary scientist for Webb. Webb’s extremely stable and precise image quality permits these very faint rings to be detected so close to Neptune.

Neptune has fascinated researchers since its discovery in 1846. Located 30 times farther from the Sun than Earth, Neptune orbits in the remote, dark region of the outer solar system. At that extreme distance, the Sun is so small and faint that high noon on Neptune is similar to a dim twilight on Earth.

This planet is characterized as an ice giant due to the chemical make-up of its interior. Compared to the gas giants, Jupiter and Saturn, Neptune is much richer in elements heavier than hydrogen and helium. This is readily apparent in Neptune’s signature blue appearance in Hubble Space Telescope images at visible wavelengths, caused by small amounts of gaseous methane.

Webb’s Near-Infrared Camera (NIRCam) images objects in the near-infrared range from 0.6 to 5 microns, so Neptune does not appear blue to Webb. In fact, the methane gas so strongly absorbs red and infrared light that the planet is quite dark at these near-infrared wavelengths, except where high-altitude clouds are present. Such methane-ice clouds are prominent as bright streaks and spots, which reflect sunlight before it is absorbed by methane gas. Images from other observatories, including the Hubble Space Telescope and the W.M. Keck Observatory, have recorded these rapidly evolving cloud features over the years.

More subtly, a thin line of brightness circling the planet’s equator could be a visual signature of global atmospheric circulation that powers Neptune’s winds and storms. The atmosphere descends and warms at the equator, and thus glows at infrared wavelengths more than the surrounding, cooler gases.

Neptune’s 164-year orbit means its northern pole, at the top of this image, is just out of view for astronomers, but the Webb images hint at an intriguing brightness in that area. A previously-known vortex at the southern pole is evident in Webb’s view, but for the first time Webb has revealed a continuous band of high-latitude clouds surrounding it.

Webb also captured seven of Neptune’s 14 known moons. Dominating this Webb portrait of Neptune is a very bright point of light sporting the signature diffraction spikes seen in many of Webb’s images, but this is not a star. Rather, this is Neptune’s large and unusual moon, Triton.

Covered in a frozen sheen of condensed nitrogen, Triton reflects an average of 70 percent of the sunlight that hits it. It far outshines Neptune in this image because the planet’s atmosphere is darkened by methane absorption at these near-infrared wavelengths. Triton orbits Neptune in an unusual backward (retrograde) orbit, leading astronomers to speculate that this moon was originally a Kuiper belt object that was gravitationally captured by Neptune. Additional Webb studies of both Triton and Neptune are planned in the coming year.

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Meteoroid impacts on Mars heard by NASA’s InSight

Newswand: NASA’s InSight has ‘heard’ its first meteoroid impacts on Mars. NASA’s InSight lander has detected seismic waves from four space rocks that crashed on Mars in 2020 and 2021.

Photo credit: NASA/JPL-Caltech/University of Arizona

 Not only do these represent the first impacts detected by the spacecraft’s seismometer since InSight touched down on the Red Planet in 2018, it also marks the first time seismic and acoustic waves from an impact have been detected on Mars.

A new paper published in Nature Geoscience details the impacts, which ranged between 53 and 180 miles (85 and 290 kilometers) from InSight’s location, a region of Mars called Elysium Planitia.

The first of the four confirmed meteoroids – the term used for space rocks before they hit the ground – made the most dramatic entrance: It entered Mars’ atmosphere on Sept. 5, 2021, exploding into at least three shards that each left a crater behind.

Then, NASA’s Mars Reconnaissance Orbiter flew over the estimated impact site to confirm the location. The orbiter used its black-and-white Context Camera to reveal three darkened spots on the surface. After locating these spots, the orbiter’s team used the High-Resolution Imaging Science Experiment camera, or HiRISE, to get a color close-up of the craters (the meteoroid could have left additional craters in the surface, but they would be too small to see in HiRISE’s images).

“After three years of InSight waiting to detect an impact, those craters looked beautiful,” said Ingrid Daubar of Brown University, a co-author of the paper and a specialist in Mars impacts.

After combing through earlier data, scientists confirmed three other impacts had occurred on May 27, 2020; Feb. 18, 2021; and Aug. 31, 2021.

Researchers have puzzled over why they haven’t detected more meteoroid impacts on Mars. The Red Planet is next to the solar system’s main asteroid belt, which provides an ample supply of space rocks to scar the planet’s surface. Because Mars’ atmosphere is just 1% as thick as Earth’s, more meteoroids pass through it without disintegrating.

InSight’s seismometer has detected over 1,300 marsquakes. Provided by France’s space agency, the Centre National d’Études Spatiales, the instrument is so sensitive that it can detect seismic waves from thousands of miles away. But the Sept. 5, 2021, event marks the first time an impact was confirmed as the cause of such waves.

InSight’s team suspects that other impacts may have been obscured by noise from wind or by seasonal changes in the atmosphere. But now that the distinctive seismic signature of an impact on Mars has been discovered, scientists expect to find more hiding within InSight’s nearly four years of data.

Science behind the strikes

Seismic data offer various clues that will help researchers better understand the Red Planet. Most marsquakes are caused by subsurface rocks cracking from heat and pressure. Studying how the resulting seismic waves change as they move through different material provides scientists a way to study Mars’ crust, mantle, and core.

The four meteoroid impacts confirmed so far produced small quakes with a magnitude of no more than 2.0. Those smaller quakes provide scientists with only a glimpse into the Martian crust, while seismic signals from larger quakes, like the magnitude 5 event that occurred in May 2022, can also reveal details about the planet’s mantle and core.

But the impacts will be critical to refining Mars’ timeline. “Impacts are the clocks of the solar system,” said the paper’s lead author, Raphael Garcia of Institut Supérieur de l’Aéronautique et de l’Espace in Toulouse, France. “We need to know the impact rate today to estimate the age of different surfaces.”

Scientists can approximate the age of a planet’s surface by counting its impact craters: The more they see, the older the surface. By calibrating their statistical models based on how often they see impacts occurring now, scientists can then estimate how many more impacts happened earlier in the solar system’s history.

InSight’s data, in combination with orbital images, can be used to rebuild a meteoroid’s trajectory and the size of its shock wave. Every meteoroid creates a shock wave as it hits the atmosphere and an explosion as it hits the ground. These events send sound waves through the atmosphere. The bigger the explosion, the more this sound wave tilts the ground when it reaches InSight. The lander’s seismometer is sensitive enough to measure how much the ground tilts from such an event and in what direction.

The lander still has time to study Mars. Dust buildup on the lander’s solar panels is reducing its power and will eventually lead to the spacecraft shutting down. Predicting precisely when is difficult, but based on the latest power readings, engineers now believe the lander could shut down between October of this year and January 2023.

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At least 70% of Martian lakes are yet to be discovered

Newswand: Lakes are bodies of water fed by rainfall, snowmelt, rivers and groundwater, through which, Earth is teeming with life. Lakes also contain critical geologic records of past climates.

Photo credit: ESA/JPL/NASA/ASU/MSSS

Though Mars is a frozen desert today, scientists have shown that Mars contains evidence of ancient lakes that existed billions of years ago, which could contain evidence for ancient life and climate conditions on the red planet. Through a meta-analysis of years of satellite data that shows evidence for lakes on Mars, Dr Joseph MICHALSKI, a geologist in the Department of Earth Sciences, The University of Hong Kong (HKU) proposed that scientists might have dramatically underestimated the number of ancient Martian lakes that once existed.

Michalski and the international team recently published their results in Nature Astronomy, which describe a global analysis of ancient Martian lakes. “We know of approximately 500 ancient lakes deposited on Mars, but nearly all the lakes we know about are larger than 100 km2,” explains Michalski. “But on Earth, 70% of the lakes are smaller than this size, occurring in cold environments where glaciers have retreated. These small-sized lakes are difficult to identify on Mars by satellite remote sensing, but many small lakes probably did exist. It is likely that at least 70% of Martian lakes have yet to be discovered.” Scientists monitor these small lakes on Earth in order to understand climate change. The missing small lakes on Mars might also contain critical information about past climates.

The recent paper also reports that most known Martian lakes date to a period 3,500 to 4,000 million years ago, but each of the lakes might have lasted only a geologically short time (10,000 to 100,000 years) during this time span. This means that ancient Mars was probably mostly cold and dry as well, but it warmed episodically for short periods of time. Michalski adds, “Because of the lower gravity on Mars and the pervasive, fine-grained soil, lakes on Mars would have been very murky and might not have allowed light to penetrate very deeply, which could present a challenge to photosynthetic life, if it existed.”

Lakes contain water, nutrients and energy sources for possible microbial life, including light for photosynthesis. Therefore, lakes are the top targets for astrobiological exploration by Mars Rovers such as NASA’s Perseverance rover now on Mars. But Michalski warns, “Not all lakes are created equal. In other words, some Martian lakes would be more interesting for microbial life than others because some of the lakes were large, deep, long-lived and had a wide range of environments such as hydrothermal systems that could have been conducive to the formation of simple life.” From this point of view, it might make sense to target large, ancient, environmentally diverse lakes for future exploration.

“Earth is host to many environments that can serve as analogs to other planets. From the harsh terrain of Svalbard to the depths of Mono Lake – we can determine how to design tools for detecting life elsewhere right here at home. Most of those tools are aimed at detecting the remains and residues of microbial life,” said Dr David BAKER, an ecologist at HKU School of Biological Sciences who is well-informed about the Earth’s microbial systems in lakes.

China successfully landed its first lander, Zhurong, on Mars in May this year. Zhurong is currently roving the plains of Utopia Planitia, exploring mineralogical and chemical clues to recent climate change. China is also planning a sample return mission likely to occur at the end of this decade, which could target one of the interesting lake deposits.

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Perseverance trying to find signs of ancient microbial life on Mars

Newswand: NASA’s Perseverance rover is trying to find signs of ancient microbial life on Mars. It is collecting rock-core samples from features within an area long considered by scientists to be a top prospect for finding signs of ancient microbial life on the Red planet. The rover has collected four samples from an ancient river delta in the Red Planet’s Jezero Crater since July 7, bringing the total count of scientifically compelling rock samples to 12.

Photo credit: NASA

“We picked the Jezero Crater for Perseverance to explore because we thought it had the best chance of providing scientifically excellent samples – and now we know we sent the rover to the right location,” said Thomas Zurbuchen, NASA’s associate administrator for science in Washington. “These first two science campaigns have yielded an amazing diversity of samples to bring back to Earth by the Mars Sample Return campaign.”

Twenty-eight miles (45 kilometers) wide, Jezero Crater hosts a delta – an ancient fan-shaped feature that formed about 3.5 billion years ago at the convergence of a Martian river and a lake. Perseverance is currently investigating the delta’s sedimentary rocks, formed when particles of various sizes settled in the once-watery environment. During its first science campaign, the rover explored the crater’s floor, finding igneous rock, which forms deep underground from magma or during volcanic activity at the surface. 

“The delta, with its diverse sedimentary rocks, contrasts beautifully with the igneous rocks – formed from crystallization of magma – discovered on the crater floor,” said Perseverance project scientist Ken Farley of Caltech in Pasadena, California. “This juxtaposition provides us with a rich understanding of the geologic history after the crater formed and a diverse sample suite. For example, we found a sandstone that carries grains and rock fragments created far from Jezero Crater – and a mudstone that includes intriguing organic compounds.”

“Wildcat Ridge” is the name given to a rock about 3 feet (1 meter) wide that likely formed billions of years ago as mud and fine sand settled in an evaporating saltwater lake. On July 20, the rover abraded some of the surface of Wildcat Ridge so it could analyze the area with the instrument called Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals, or SHERLOC. 

SHERLOC’s analysis indicates the samples feature a class of organic molecules that are spatially correlated with those of sulfate minerals. Sulfate minerals found in layers of sedimentary rock can yield significant information about the aqueous environments in which they formed.

What is organic matter?

Organic molecules consist of a wide variety of compounds made primarily of carbon and usually include hydrogen and oxygen atoms. They can also contain other elements, such as nitrogen, phosphorus, and sulfur. While there are chemical processes that produce these molecules that don’t require life, some of these compounds are the chemical building blocks of life. The presence of these specific molecules is considered to be a potential biosignature – a substance or structure that could be evidence of past life but may also have been produced without the presence of life.

In 2013, NASA’s Curiosity Mars rover found evidence of organic matter in rock-powder samples, and Perseverance has detected organics in Jezero Crater before. But unlike that previous discovery, this latest detection was made in an area where, in the distant past, sediment and salts were deposited into a lake under conditions in which life could potentially have existed. In its analysis of Wildcat Ridge, the SHERLOC instrument registered the most abundant organic detections on the mission to date. 

“In the distant past, the sand, mud, and salts that now make up the Wildcat Ridge sample were deposited under conditions where life could potentially have thrived,” said Farley. “The fact the organic matter was found in such a sedimentary rock – known for preserving fossils of ancient life here on Earth – is important. However, as capable as our instruments aboard Perseverance are, further conclusions regarding what is contained in the Wildcat Ridge sample will have to wait until it’s returned to Earth for in-depth study as part of the agency’s Mars Sample Return campaign.”

The first step in the NASA-ESA (European Space Agency) Mars Sample Return campaign began when Perseverance cored its first rock sample in September 2021. Along with its rock-core samples, the rover has collected one atmospheric sample and two witness tubes, all of which are stored in the rover’s belly.

The geologic diversity of the samples already carried in the rover is so good that the rover team is looking into depositing select tubes near the base of the delta in about two months. After depositing the cache, the rover will continue its delta explorations.

“I’ve studied Martian habitability and geology for much of my career and know first-hand the incredible scientific value of returning a carefully collected set of Mars rocks to Earth,” said Laurie Leshin, director of NASA’s Jet Propulsion Laboratory in Southern California. “That we are weeks from deploying Perseverance’s fascinating samples and mere years from bringing them to Earth so scientists can study them in exquisite detail is truly phenomenal. We will learn so much.”

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Missing moon may be the reason for tilt of Saturn

Newswand: A new study on the tilt of Saturn has presumed that a missing moon of the planet was the reason for the tilt of it.

Swirling around the planet’s equator, the rings of Saturn are a dead giveaway that the planet is spinning at a tilt. The belted giant rotates at a 26.7-degree angle relative to the plane in which it orbits the Sun. Astronomers have long suspected that this tilt comes from gravitational interactions with its neighbor Neptune, as Saturn’s tilt precesses, like a spinning top, at nearly the same rate as the orbit of Neptune.

But a new modeling study by astronomers at MIT and elsewhere has found that, while the two planets may have once been in sync, Saturn has since escaped Neptune’s pull. What was responsible for this planetary realignment? The team has one meticulously tested hypothesis: a missing moon.

In a study appearing in Science, the team proposes that Saturn, which today hosts 83 moons, once harbored at least one more, an extra satellite that they name Chrysalis. Together with its siblings, the researchers suggest, Chrysalis orbited Saturn for several billion years, pulling and tugging on the planet in a way that kept its tilt, or “obliquity,” in resonance with Neptune.

But around 160 million years ago, the team estimates, Chrysalis became unstable and came too close to its planet in a grazing encounter that pulled the satellite apart. The loss of the moon was enough to remove Saturn from Neptune’s grasp and leave it with the present-day tilt.

What’s more, the researchers surmise, while most of Chrysalis’ shattered body may have made impact with Saturn, a fraction of its fragments could have remained suspended in orbit, eventually breaking into small icy chunks to form the planet’s signature rings.

The missing satellite, therefore, could explain two longstanding mysteries: Saturn’s present-day tilt and the age of its rings, which were previously estimated to be about 100 million years old — much younger than the planet itself.

“Just like a butterfly’s chrysalis, this satellite was long dormant and suddenly became active, and the rings emerged,” says Jack Wisdom, professor of planetary sciences at MIT and lead author of the new study.

The study’s co-authors include Rola Dbouk at MIT, Burkhard Militzer of the University of California at Berkeley, William Hubbard at the University of Arizona, Francis Nimmo and Brynna Downey of the University of California at Santa Cruz, and Richard French of Wellesley College.

A moment of progress

In the early 2000s, scientists put forward the idea that Saturn’s tilted axis is a result of the planet being trapped in a resonance, or gravitational association, with Neptune. But observations taken by NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, put a new twist on the problem. Scientists found that Titan, Saturn’s largest satellite, was migrating away from Saturn at a faster clip than expected, at a rate of about 11 centimeters per year. Titan’s fast migration, and its gravitational pull, led scientists to conclude that the moon was likely responsible for tilting and keeping Saturn in resonance with Neptune.

But this explanation hinges on one major unknown: Saturn’s moment of inertia, which is how mass is distributed in the planet’s interior. Saturn’s tilt could behave differently, depending on whether matter is more concentrated at its core or toward the surface.

“To make progress on the problem, we had to determine the moment of inertia of Saturn,” Wisdom says.

The lost element

In their new study, Wisdom and his colleagues looked to pin down Saturn’s moment of inertia using some of the last observations taken by Cassini in its “Grand Finale,” a phase of the mission during which the spacecraft made an extremely close approach to precisely map the gravitational field around the entire planet.  The gravitational field can be used to determine the distribution of mass in the planet.

Wisdom and his colleagues modeled the interior of Saturn and identified a distribution of mass that matched the gravitational field that Cassini observed. Surprisingly, they found that this newly identified moment of inertia placed Saturn close to, but just outside the resonance with Neptune. The planets may have once been in sync, but are no longer.

“Then we went hunting for ways of getting Saturn out of Neptune’s resonance,” Wisdom says.

The team first carried out simulations to evolve the orbital dynamics of Saturn and its moons backward in time, to see whether any natural instabilities among the existing satellites could have influenced the planet’s tilt. This search came up empty.

So, the researchers reexamined the mathematical equations that describe a planet’s precession, which is how a planet’s axis of rotation changes over time. One term in this equation has contributions from all the satellites. The team reasoned that if one satellite were removed from this sum, it could affect the planet’s precession.

The question was, how massive would that satellite have to be, and what dynamics would it have to undergo to take Saturn out of Neptune’s resonance?

Wisdom and his colleagues ran simulations to determine the properties of a satellite, such as its mass and orbital radius, and the orbital dynamics that would be required to knock Saturn out of the resonance.

They conclude that Saturn’s present tilt is the result of the resonance with Neptune and that the loss of the satellite, Chrysalis, which was about the size of Iapetus, Saturn’s third-largest moon, allowed it to escape the resonance.

Sometime between 200 and 100 million years ago, Chrysalis entered a chaotic orbital zone, experienced a number of close encounters with Iapetus and Titan, and eventually came too close to Saturn, in a grazing encounter that ripped the satellite to bits, leaving a small fraction to circle the planet as a debris-strewn ring.

The loss of Chrysalis, they found, explains Saturn’s precession, and its present-day tilt, as well as the late formation of its rings.

“It’s a pretty good story, but like any other result, it will have to be examined by others,” Wisdom says. “But it seems that this lost satellite was just a chrysalis, waiting to have its instability.”

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