Thanks to satellite imagery, we now know that both Mars and the moon also have lava tubes and skylights. These caves and holes likely formed the same way they do on Earth. As a channel of molten lava flows, its top layer, exposed to air, cools and forms a crust. Below, the hotter lava continues to course until it empties out, leaving behind a tube-like cave. Skylights form when parts of the lava tube ceiling collapse. Sometimes these ceilings crumble and completely block access to the cave. Other times, they fall away clean, leaving pits with dangerous, potentially unstable overhangs. But once in a while, the rocks fall in such a way to give unfettered access to a lava-carved tunnel.

NASA research indicates hunks of frozen carbon dioxide—dry ice—may glide down some Martian sand dunes on cushions of gas similar to miniature hovercraft, plowing furrows as they go. Researchers deduced this process could explain one enigmatic class of gullies seen on Martian sand dunes by examining images from NASA's Mars Reconnaissance Orbiter (MRO) and performing experiments on sand dunes in Utah and California. "I have always dreamed of going to Mars," said Serina Diniega, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and lead author of a report published online by the journal Icarus. "Now I dream of snowboarding down a Martian sand dune on a block of dry ice."

When Jupiter’s tides ripped Comet Shoemaker–Levy 9 to shreds, only for the icy chunks to succumb to the intense Jovian gravity, ultimately slamming into the gas giant’s atmosphere, mankind was treated to a rare cosmic spectacle (in human timescales at least). That was the first time in modern history that we saw a comet do battle with a planet… and lose. But next year, astronomers think there’s a chance — albeit a small one — of a neighboring planet getting punched by an icy interplanetary interloper. However, this planet doesn’t have a generously thick atmosphere to soften the blow. Rather than causing bruises in a dense, molecular hydrogen atmosphere, this comet will pass through the atmosphere like it wasn’t even there and hit the planetary surface like a cosmic pile-driver, ripping into the crust. What’s more, we’d have robotic eyes on the ground and in orbit should the worst happen.

Asteroid impacts are among the most feared of natural catastrophes. So estimating the risk they pose to humanity is an important task. One method is to look at the number of impacts in the past and use this as a guide to the future. This isn’t entirely straightforward since the distribution of crater sizes we see today depends not only on the rate of impact in the past but also on the rate of disappearance via processes such as erosion, tectonic changes, obliteration by other craters and so on. Nevertheless, various groups have measured the distribution of crater sizes and come up with estimates of future impact probabilities. Today. William Bruckman and pals at the University of Puerto Rico at Humacao do exactly this kind of analysis but with a twist. They derive impact probabilities for Earth but also for Mars. Their conclusion is that astronauts visiting Mars for just a few years are likely to witness a significant asteroid impact.

Christine Hartland’s gifted/self-contained classroom of fifth-graders has been working on a hypothesis about global warming on Mars since the school year began. As the only class at Kyrene Monte Vista Elementary, and likely the district, in the Mars Student Imaging Program, the students have been doing work that is usually reserved for high school students. The class came up with their own questions, narrowed them down to one, and began working on collecting real data about pit-like surface holes on Mars’ ground.

The soil on Mars appears to be very similar to the volcanic soils of Hawaii, according to scientists at the National Aeronautics and Space Administration, NASA. The results come after the first chemical and mineralogy tests performed on Martian soil scooped up and taken aboard NASA’s Mars rover, Curiosity. NASA said the soil analysis was carried out by the rover’s Chemistry and Mineralogy instrument (CheMin). The U.S. space agency said the study concluded that the Mars soil sample “is similar to weathered basaltic soils of volcanic origin in Hawaii.”

Dramatic images going wide for the first time tell a surprising tale of Martian eruptions. The pictures doing the dazzling today were shot by the Mars Reconnaissance Orbiter (MRO) in 2010 and show the predictable — if beautiful — rusty dunes of the Martian surface, sculpted like snowdrifts from the planet’s tenuous but persistent wind. The scene is broken up, however, buy strange, black, spidery blemishes scattered randomly about. From orbit they look tiny, but on the ground they’d be huge — surely larger than a football field. It’s partly their very ugliness that makes them eye-catching and partly the mystery of what causes them. Actually, however, that last part is likely no mystery at all — and the source of the features is one more indication of how complex a planet Mars is turning out to be.

NASA's Curiosity rover mission has found evidence a stream once ran vigorously across the area on Mars where the rover is driving. There is earlier evidence for the presence of water on Mars, but this evidence -- images of rocks containing ancient streambed gravels -- is the first of its kind. Scientists are studying the images of stones cemented into a layer of conglomerate rock. The sizes and shapes of stones offer clues to the speed and distance of a long-ago stream's flow. "From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep," said Curiosity science co-investigator William Dietrich of the University of California, Berkeley. "Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them. This is the first time we're actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it."

NASA's Curiosity rover found evidence for an ancient, flowing stream on Mars at a few sites, including the rock outcrop pictured here, which the science team has named "Hottah" after Hottah Lake in Canada's Northwest Territories. It may look like a broken sidewalk, but this geological feature on Mars is actually exposed bedrock made up of smaller fragments cemented together, or what geologists call a sedimentary conglomerate. Scientists theorize that the bedrock was disrupted in the past, giving it the titled angle, most likely via impacts from meteorites. The key evidence for the ancient stream comes from the size and rounded shape of the gravel in and around the bedrock. Hottah has pieces of gravel embedded in it, called clasts, up to a couple inches (few centimeters) in size and located within a matrix of sand-sized material. Some of the clasts are round in shape, leading the science team to conclude they were transported by a vigorous flow of water. The grains are too large to have been moved by wind.

Curiosity, the NASA rover that landed on Mars last month, is sending us remarkable weather observations from the Martian surface that are attracting interest from scientists. “From a weather point of view, Mars is the most ‘Earth-like’ of the other planets in our solar system, and many features of the weather there are similar to Earth,” says Kevin Hamilton, a pioneer in the area of computer modeling of the Martian atmosphere. Hamilton, who is Director of UH Manoa’s International Pacific Research Center and a Professor of Meteorology, noted that Curiosity is the fifth ‘Weather Station’ on Mars. Over the last 35 years, a total of four NASA probes had reached the Martian surface and returned weather data. “These earlier observations had shown a large daily cycle in temperature and air pressure on Mars. The atmospheric temperature near the surface of Mars generally varies by more than 100°F between day and night because of the overall thinner Martian atmosphere and lack of oceans and their moderating influence,” says Hamilton

Scientists are beginning to sketch out plans for NASA's new Mars rover Curiosity to climb Mount Sharp, but future robots may have a more direct way to access the planet's history books. Recent discoveries of "skylights" (pictured here) and lava tubes on the surface of Mars, as well as the moon, are sparking the development of robotic probes that can descend into caves and explore tunnels. "Geology works in layers, so how many layers can you see? Well, we know there are sinkholes on Mars. Those sinkholes expose potentially hundreds of feet of layers, so if you could lower something down and examine those layers and explore a tunnel underneath, or anything of that sort, the science that can be done with that is just phenomenal," Jason Derleth, senior technology analyst with NASA's Innovative Advanced Concepts Program, told Discovery News.

For years, many scientists had thought that plate tectonics existed nowhere in our solar system but on Earth. Now, a UCLA scientist has discovered that the geological phenomenon, which involves the movement of huge crustal plates beneath a planet's surface, also exists on Mars. "Mars is at a primitive stage of plate tectonics. It gives us a glimpse of how the early Earth may have looked and may help us understand how plate tectonics began on Earth," said An Yin, a UCLA professor of Earth and space sciences and the sole author of the new research. Yin made the discovery during his analysis of satellite images from THEMIS (Thermal Emission Imaging System), an instrument on board the Mars Odyssey spacecraft, and from the HIRISE (High Resolution Imaging Science Experiment) camera on NASA's Mars Reconnaissance Orbiter. He analyzed about 100 satellite images — approximately a dozen were revealing of plate tectonics.

When solar storms strike Earth, as they have this week, the planet's magnetic field is a first line of defense against fast-moving clouds of charged particles hurtling from the sun. A new study hints at how important that line of defense is in fostering a livable planet. During a bout of turbulence in the solar wind in 2008, researchers found that Mars lost oxygen atoms in its atmosphere 10 times faster than did Earth – an observation the team attributes at least in part to the relative strength of each planet's magnetic field. It marks the first time researchers have measured the effects of the solar wind on two planets at the same time and under the same windy conditions, and there is hope that the study can be extended to Venus, which has no magnetic field at all.

ESA's Mars Express has returned strong evidence for an ocean once covering part of Mars. Using radar, it has detected sediments reminiscent of an ocean floor within the boundaries of previously identified, ancient shorelines on Mars. The MARSIS radar was deployed in 2005 and has been collecting data ever since. Jérémie Mouginot, Institut de Planétologie et d'Astrophysique de Grenoble (IPAG) and the University of California, Irvine, and colleagues have analysed more than two years of data and found that the northern plains are covered in low-density material. "We interpret these as sedimentary deposits, maybe ice-rich," says Dr Mouginot. "It is a strong new indication that there was once an ocean here."

The sun battered the Earth's magnetosphere with an "epic" geomagnetic storm over the last couple of days, generating beautiful auroral displays at low latitudes. Now it's Mars' turn. On Saturday (Oct. 22), a large bubble of solar plasma was blasted from the sun's surface. Unlike the coronal mass ejection (CME) that struck us on Monday, Saturday's CME was sent in a different direction -- toward the Red Planet. As per simulations carried out by NASA's Goddard Space Weather Laboratory (shown below), the CME should have arrived in Mars orbit by now (Oct. 26). However, its impact on Mars will be very different than a CME's impact on Earth.