Moon, Mercury, Jupiter and Mars
Credit: Mike Salway
The large impact crater known as Stickney is the largest crater on the Martian moon Phobos.
Credit: NASA/JPL-Caltech/University of Arizona
This image shows the recent observations of the planets Mars and Saturn made with the NASA/ESA Hubble Space Telescope. The observations of both objects were made in June and July 2018 and show the planets close to their opposition.
Credit: NASA/ESA, Hubble
A ground-penetrating radar aboard the European Space Agency’s Mars Express satellite has found evidence for a pool of liquid water, a potentially habitable environment, buried under layers of ice and dust at the red planet’s south pole.
“This subsurface anomaly on Mars has radar properties matching water or water-rich sediments,” said Roberto Orosei, principal investigator of the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument, or MARSIS, lead author of a paper in the journal Science describing the discovery.
The conclusion is based on observations of a relatively small area of Mars, but “it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered,” added Orosei.
Scientists have long theorised the presence of subsurface pools under the martian poles where the melting point of water could be decreased due to the weight of overlying layers of ice. The presence of salts in the Martian soil also would act to reduce the melting point and, perhaps, keep water liquid even at sub-freezing temperatures.
Earlier observations by MARSIS were inconclusive, but researchers developed new techniques to improve resolution and accuracy.
“We’d seen hints of interesting subsurface features for years but we couldn’t reproduce the result from orbit to orbit, because the sampling rates and resolution of our data was previously too low,” said Andrea Cicchetti, MARSIS operations manager.
“We had to come up with a new operating mode to bypass some onboard processing and trigger a higher sampling rate and thus improve the resolution of the footprint of our dataset. Now we see things that simply were not possible before.”
MARSIS works by firing penetrating radar beams at the surface of Mars and then measuring the strength of the signals as they are reflected back to the spacecraft.
The data indicating water came from a 200-kilometre-wide (124-mile-wide) area that shows the south polar region features multiple layers of ice and dust down to a depth of about 1.5 kilometres (0.9 miles). A particularly bright reflection below the layered deposits can be seen in a zone measuring about 20 kilometres (12 miles) across.
Orosei’s team interprets the bright reflection as the interface between overlying ice and a pool or pond of liquid water. The pool must be at least several centimetres thick for the MARSIS instrument to detect it.
“The long duration of Mars Express, and the exhausting effort made by the radar team to overcome many analytical challenges, enabled this much-awaited result, demonstrating that the mission and its payload still have a great science potential,” says Dmitri Titov, ESA’s Mars Express project scientist.
The discovery is significant because it raises the possibility, at least, of potentially habitable sub-surface environments.
“Some forms of microbial life are known to thrive in Earth’s subglacial environments, but could underground pockets of salty, sediment-rich liquid water on Mars also provide a suitable habitat, either now or in the past?” ESA asked in a statement. “Whether life has ever existed on Mars remains an open question.”
Auroras appear on Earth as ghostly displays of colorful light in the night sky, usually near the poles. Our rocky neighbor Mars has auroras too, and NASA’s MAVEN spacecraft just found a new type of Martian aurora that occurs over much of the day side of the Red Planet, where auroras are very hard to see.
Auroras flare up when energetic particles plunge into a planet’s atmosphere, bombarding gases and making them glow. While electrons generally cause this natural phenomenon, sometime protons can elicit the same response, although it’s more rare. Now, the MAVEN team has learned that protons were doing at Mars the same thing as electrons usually do at Earth—create aurora. This is especially true when the Sun ejects a particularly strong pulse of protons, which are hydrogen atoms stripped of their lone electrons by intense heat. The Sun ejects protons at speeds up to two million miles per hour (more than 3 million kilometers per hour) in an erratic flow called the solar wind.
The MAVEN (Mars Atmosphere and Volatile Evolution mission) team was studying Mars’ atmosphere with the Imaging UltraViolet Spectrograph (IUVS), and observed that on occasion, the ultraviolet light coming from hydrogen gas in Mars’ upper atmosphere would mysteriously brighten for a few hours. They then noticed that the brightening events occurred when another MAVEN instrument, the Solar Wind Ion Analyzer (SWIA), measured enhanced solar wind protons.
But two puzzles make this type of aurora seem impossible at first glance: how did these protons get past the planet’s “bow shock,” a magnetic obstacle which normally diverts the solar wind’s charged particles around the planet? And how could the protons give off light, since atoms need electrons to do so?
“The answer was thievery,” said Justin Deighan, of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder, lead author of a paper on this research appearing July 23 in Nature Astronomy. “As they approach Mars, the protons coming in with the solar wind transform into neutral atoms by stealing electrons from the outer edge of the huge cloud of hydrogen surrounding the planet. The bow shock can only divert charged particles, so these neutral atoms continue right on through.” When those high-speed incoming atoms hit the atmosphere, some of their energy was emitted as ultraviolet light, which is invisible to the human eye but detectable to instruments like the IUVS on MAVEN. In fact, one incoming atom can collide with molecules in the atmosphere hundreds of times before it slows down, giving off a slew of ultraviolet photons.
“The Martian proton auroras are more than a light show,” said Jasper Halekas of the University of Iowa, responsible for the SWIA instrument. “They reveal that the solar wind is not completely diverted around Mars, by showing how solar wind protons can sneak past the bow shock and impact the atmosphere, depositing energy and even enhancing the hydrogen content there.”
Proton auroras do occur at Earth, but not as often as at Mars. One key difference is Earth’s strong magnetic field, which diverts the solar wind away from Earth to a much greater degree than at Mars. On Earth, proton auroras only occur in very small regions near the poles, whereas at Mars they can happen everywhere.
However, proton auroras could be common on Venus and on Saturn’s moon Titan. Like Mars, these two worlds lack their own magnetic fields, and have lots of hydrogen in their upper atmospheres—with plenty of electrons to share. Looking further, it’s likely that many planets orbiting other stars have the same favorable conditions, and would be likely to have proton auroras too.
This research was funded by the MAVEN mission. MAVEN’s principal investigator is based at the University of Colorado’s Laboratory for Atmospheric and Space Physics, Boulder, and NASA Goddard manages the MAVEN project.
Venus, Jupiter and Mars at Dawn – Oct 22, 2015
Image credit: Joseph Brimacombe
Images of Mars taken by the Mars Express spacecraft
Credit: ESA / DLR / FU Berlin / Kevin M. Gill
A self-portrait by NASA’s Curiosity rover taken on Sol 2082 (June 15, 2018). A Martian dust storm has reduced sunlight and visibility at the rover’s location in Gale Crater. A drill hole can be seen in the rock to the left of the rover at a target site called “Duluth.”
Dunes on Mars captured by NASA’s Mars Reconnaissance Orbiter (MRO)
It’s storm season on Mars. Dusty with a chance of dust is the weather report for Gale crater as a recent planet-scale dust storm rages. On June 10 looking toward the east-northeast crater rim, the Curiosity rover’s Mastcam captured this image of its local conditions so far. Meanwhile over 2,000 kilometers away, the Opportunity rover ceased science operations as the storm grew thicker at its location on the west rim of Endeavour crater, and has stopped communicating, waiting out the storm for now. Curiosity is powered by a radioisotope thermoelectric generator, but the smaller Opportunity rover uses solar panels to charge its batteries. For Opportunity, the increasingly severe lack of sunlight has caused its batteries to run low.
This set of images from NASA’s Mars Reconnaissance Orbiter shows a fierce dust storm is kicking up on Mars, with rovers on the surface indicated as icons.
This series of images shows simulated views of a darkening Martian sky blotting out the Sun from NASA’s Opportunity rover’s point of view, with the right side simulating Opportunity’s current view in the global dust storm (June 2018).