RSSArchive for September, 2010

Moon’s face is a history book

Artist's impression of LRO

Artist's impression of the NASA's Lunar Reconnaissance Orbiter spacecraft, which has been mapping the Moon with unprecedented precision.

  • Moon’s craters came from bombardment by impactors
  • Now, first comprehensive map of craters has been made
  • Shows the bombardment changed dramatically at a certain stage

Take a cursory look at the Moon, and it can resemble a pockmarked golf ball. The dimples and divots on its surface are testament that our satellite has withstood a barrage of impacts from comets, asteroids and other space matter throughout much of its history.

Because the geological record of that pummelling remains largely intact, scientists have used the Moon to help reconstruct the history of the chaotic early days of the inner Solar System.

Now a team led by Brown University planetary geologists has produced the first uniform, comprehensive catalogue of large lunar craters…which could help shed light on the full-scale, planetary bombardment suffered by the planets of the inner Solar System more than 4 billion years ago.

In a paper appearing in the journal Science, the team used data from the Lunar Orbiter Laser Altimeter (LOLA), one of a suite of instruments aboard NASA’s Lunar Reconnaissance Orbiter, to identify and map 5,185 craters that are 20 kilometres in diameter or larger.

Map of craters on the Moon

A research team mapped nearly 5,200 craters on the Moon, the first global catalogue of large craters on the lunar surface. The analysis could shed light on planetary bombardment in the inner Solar System more than 4 billion years ago.

From the crater count and analysis, the team (which includes scientists from the Massachusetts Institute of Technology and the NASA Goddard Space Flight Centre) determined the Moon’s oldest regions are the southern near side and the north-central far side.

The group also confirmed that the South Pole–Aitken Basin is the oldest basin, meaning that any samples from there could be invaluable to further understanding the Moon and other bodies of the inner Solar System.

Rethinking the Moon’s bombardment

A major finding deals with the stream of projectiles pinballing throughout the inner Solar System in its earliest days.

For years, the prevailing wisdom was that the Moon was buffeted by a volley of space matter that held a steady ratio between larger and smaller objects, which planetary scientists refer to as “size-frequency distribution.”

The bombardment activity has never been questioned. But in 2005, the size-frequency distribution part of it was challenged. In a paper in Science, a group led by University of Arizona geologist Robert Strom hypothesised that the ratio of larger and smaller objects striking the Moon had differed during its first billion years of existence.

The Brown-led team’s crater analysis lends added credence to that hypothesis.

The researchers studied impact craters formed early in the Moon’s history (when major basins were created by large projectiles striking the surface) and compared them with those they knew were formed later (when objects struck lava flows that had covered these basins).

Craters on the Moon

Scientists have found differences in the size range of craters on the lunar highlands compared to the lowlands.

They found that the oldest surfaces (located in the lunar highlands) bore crater markings indicating a greater ratio of larger impactors. The group looked in particular at Orientale Basin, formed by a massive impactor about 3.8 billion years ago, and determined that this is approximately when the era of larger projectiles versus smaller projectiles ended.

Much more to do

The finding opens a set of intriguing questions for what was going on in the inner Solar System leading up to roughly the time that Orientale Basin was formed.

“We know the asteroid belt has been spinning off projectiles at a relatively constant rate for three and a half billion years,” said Caleb Fassett, a postdoctoral researcher at Brown. “But now we go back earlier in the Solar System’s history, and suddenly things are completely different.”

The scientists think the change may have been caused by the gravitational pull on the asteroid belt exerted by larger planets such as Jupiter and Saturn as they settled into their orbits…or it could have been a temporary abundance of comets, an unexplained change in the size of impactors emanating from the asteroid belt, or something else.

The Lunar Orbiter Laser Altimeter measures the Moon’s surface topography with a vertical precision of 10 centimetres using laser pulses bounced off the lunar surface just 25 metres apart.

In all, the findings “are telling us something about the infancy of the Solar System,” said James W. Head III, a planetary geologist at Brown and the paper’s lead author. “It is clear we can find out and learn so much more from future missions, robotic or otherwise. There is so much to do.”

Adapted from information issued by NASA / LRO / LOLA / GSFC / MIT / Brown.

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The eruptions of Enceladus

Enceladus

Ice plumes erupting from the near the south pole of Saturn's moon Enceladus.

Barely 500 kilometres wide, Saturn’s moon Enceladus has attracted a lot of attention in recent years since the discovery of geysers shooting out from near its south pole.

NASA’s Cassini spacecraft spotted plumes, large and small, spraying water ice out from many locations along what have been dubbed “tiger stripes”…fissures in the crust that spray icy particles, water vapour and organic compounds.

The image above was taken from a distance of approximately 431,000 kilometres (268,000 miles).

In the Cassini image below, over 30 individual jets of different sizes can be seen, more than 20 of which had not been seen before the image was taken.

Enceladus

Scientists have counted over 30 individual plumes shooting out from a region of fissures on Enceladus known as the "tiger stripes".

This mosaic was created from two high-resolution images that were captured by the narrow-angle camera when NASA’s Cassini spacecraft flew past Enceladus and through the jets on November 21, 2009. Imaging the jets over time will allow Cassini scientists to study the consistency of their activity.

The view was obtained at a distance of approximately 14,000 kilometres (9,000 miles), giving a resolution of 81 metres (267 feet) per pixel.

Here’s a short video on some of the recent investigations of Enceladus.

Adapted from information issued by NASA / JPL / Space Science Institute / ESA.

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The Trifid Nebula

The Trifid Nebula

Dark "lanes" of dense interstellar dust trisect the glowing gas of the Trifid Nebula, 9,000 light-years from Earth.

Nine-thousand light-years away in the direction of the constellation Sagittarius, lies the famous Trifid Nebula, so-called for the three dark “lanes” that trisect it.

The Trifid’s triple nature is not limited to the lanes though. It is also three different types of nebulosity in one…it is a reflection, emission and dark nebula in one neat package.

A nebula is a cloud of gas and sometimes dust, floating in interstellar space.

Reflection nebulae have a bluish colour. We see them because light from nearby stars is reflecting off them—the process preferentially reflects the blue wavelengths of the starlight.

Emission nebulae are pinkish. In this case they’re not reflecting light, but emitting their own pale glow. (In the case of the image above, the emission nebulosity looks orange due to the particular wavelength observation used to make the image.)

Silhouetted against brighter backgrounds, dark nebulae stand out like ghostly holes in space. In reality they are very dense clouds of gas and dust particles—they don’t give off or reflect any light to speak of.

The Trifid was discovered in 1764 by the French astronomer Charles Messier, who made it number 20 in his catalogue of “deep sky” objects…hence it’s other common name, M 20.

Messier was a comet hunter who had become frustrated by repeatedly coming across fuzzy blobs in the sky that didn’t turn out to be comets. He decided to make a catalogue of those blobs so that he and other astronomers could learn to ignore them in future.

Ironically, he is now better known for his list of 103 deep sky objects (more were added later by other astronomers) than he is for the 13 comets he discovered.

At the time, Messier thought M 20 was actually a small bunch of stars that couldn’t quite be seen individually. But he did notice the three dark lanes running through it, and gave it the name Trifid.

Story by Jonathan Nally, editor SpaceInfo.com.au

Image courtesy IAC / Daniel López.

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Portrait of Earth and Moon

MESSENGER image of the Earth and Moon

NASA’s MESSENGER spacecraft took this image of the Earth and Moon from the distance of the orbit of Mercury, 183 million kilometres away.

Looking back from its orbit around Mercury, NASA’s Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft captured this view of Earth and the Moon on May 6, 2010.

The spacecraft was 183 million kilometres (114 million miles) from Earth at the time, farther than our average distance from the Sun (150 million kilometres, or 93 million miles) because Mercury and Earth were at different places in their orbits around the Sun.

The image was taken by the spacecraft’s Wide Angle Camera (WAC) on the Mercury Dual Imaging System (MDIS).

The view was a happy coincidence for the MESSENGER science team, as the probe was looking for vulcanoids, small rocky objects that have been postulated to hide in orbits between Mercury and the Sun.

MESSENGER is the first spacecraft to orbit Mercury since Mariner 10 in 1974-75. It is not, however, the first to get a long-distance shot of Earth. Below are some others, and you can see more of them on the Planetary Society’s site here.

Spirit rover image of Earth

In 2004, the Spirit rover on Mars snapped the first shot of our planet as viewed from the surface of another planet.

Cassini long-distance image of Earth

In 2006, Cassini sent back snapshots from 1.5 billion kilometres (930 million miles) from Earth as the spacecraft orbited Saturn. The Earth is small dot to the right of centre.

Voyager 1 pale blue dot image of Earth

And the operators of the venerable Voyager 1 spacecraft pieced together a family portrait of the entire Solar System in 1990, spying Earth from more than 6.4 billion kilometres (4 billion miles) away.

NASA image provided by the MESSENGER science team, NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington. Text adapted from information issued by Mike Carlowicz, NASA.

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Stellar cannibal hides it age well

Artist's impression of the star BP Piscium

Artist's impression of the star BP Piscium. Astronomers think it has eaten another star, with the leftover material forming a surrounding gas and dust cloud, within which new planets might form. Some of the leftover stuff is being shot out in "jets" from near the poles of the star.

  • Young looking star is actually probably quite old
  • Seems to have recently devoured a companion star
  • Leftover crumbs could be forming into planets

An astronomer may have caught a cannibalistic star in the act of devouring a companion and making a new generation of planets from the resulting cloud of leftover crumbs.

Using data from NASA’s Chandra X-ray Observatory, Joel Kastner, professor at Rochester Institute of Technology (RIT), has found evidence that a star in the constellation of Pisces—called BP Piscium, or BP Psc for short—is not the young star it appears to be, but is more likely a one billion-year-old red giant that has gobbled up a star or planet in its vicinity.

The star’s extreme properties have puzzled astronomers since Kastner and Ben Zuckerman, professor at the University of California, Los Angeles, first looked at BP Psc 15 years ago. The star is about 1,000 light-years from Earth.

False-colour image of BP Piscium

False-colour image of BP Piscium, put together using X-ray and optical wavelength observations. The two jets blasting out of the star are several light-years long.

Conflicting characteristics have caused confusion as to whether the star is young or old.

Kastner attributes the star’s potentially deceptive youthful appearance to two things: an surrounding cloud of gas and dust that resembles the sort that forms planets around young stars; and prominent “jets” extending from the poles of the star that eject material at high velocity.

A typical young star sucks in material from the surrounding cloud, incorporating about 90 percent of the material and spitting out the rest through jets or geysers shooting out in opposite directions.

Kastner and his colleagues were doubtful about the youth of the star. For one thing, the star is isolated, whereas most young stars form in clusters.

“As hard as people have looked, they have not been able to find [another] young star near BP Psc,” says Kastner, a professor in RIT’s Chester F. Carlson Centre for Imaging Science. “That was one of several things that made Ben [Zuckerman] and me suspect that it wasn’t actually young.”

Second, this enigmatic star in the Pisces constellation lacks the large abundance of lithium on its surface that is typical of young stars. Older stars lose their lithium in nuclear reactions when mixing and churning folds the gases into the centre of the star. According to Kastner, other key spectral features involving the star’s radius and surface gravity also point to the star’s advanced age.

Stellar cannibalism

Kastner is ready to close the debate with data obtained from the Chandra X-ray Observatory.

“The last piece of evidence, which, to me, is the nail in the coffin that BP Psc is old rather than young, is that its rate of X-ray production is very similar to old, yet rapidly spinning, giant stars that have surface temperatures similar to BP Psc,” Kastner says.

If BP Psc were a young star, it would emit X-rays in the hundreds, even up to a few thousand, in a day’s observing time with Chandra, Kastner notes. Instead, it is a weak X-ray source.

Artist's impression of the Chandra X-ray Observatory.

Artist's impression of NASA’s Chandra X-ray Observatory.

“We stared at BP Psc for one day with Chandra and only detected about 18 X-rays,” Kastner says. “We could almost name them.”

The rate of X-rays coming from the star are in keeping with a class of rapidly rotating old stars having similar temperature to BP Psc, Kastner says. This class is thought to be the result of one star swallowing another close companion star.

“Our working speculation is that we are observing the star right at the point at which it has swallowed its companion and hence formed a [surrounding cloud from the leftover bits],” Kastner says. “Some of the material that used to be its companion has fallen onto the star and some has been shot out at high speeds, and that’s what we’re seeing.”

The enigmatic star is likely about a billion years old and just entering the red giant stage in its life cycle in which it swells to digest its star or planet companion.

“It could be a small star or a large planet,” Kastner says. “We don’t know which it could be, but we’re very interested in finding out.”

“In order to understand the extrasolar planets that are now being discovered by the dozen, we need to figure out how planets might be forming and therefore where we should go look for them,” Kastner says. “I think this object is especially interesting because it gives us a good shot at finding young planets around an old star.”

Image credits: (X-ray) NASA / CXC / RIT / J. Kastner et al; (optical) UCO / Lick / STScI / M. Perrin et al; (illustration) CXC / M. Weiss.

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Sculptures in space

Nebulosity in the Carina Nebula

Light-year-long pillars of cold hydrogen gas and interstellar dust in the Carina Nebula.

Enjoying a frozen treat on a hot summer day can leave a sticky mess as it melts in the Sun and deforms. In the cold vacuum of space, there is no edible ice cream, but there is radiation from massive stars that is carving away at cold molecular clouds, creating bizarre, fantasy-like structures.

These one-light-year-tall pillars of cold hydrogen and dust, imaged by the Hubble Space Telescope, are located in the Carina Nebula. Violent stellar winds and powerful radiation from massive stars are sculpting the surrounding nebula. Inside the dense structures, new stars may be born.

See the full-size, high-resolution version here (new window).

This image of dust pillars in the Carina Nebula is a composite of 2005 observations taken of the region in hydrogen light (light emitted by hydrogen atoms) along with 2010 observations taken in oxygen light (light emitted by oxygen atoms), both times with Hubble’s Advanced Camera for Surveys. The immense Carina Nebula is an estimated 7,500 light-years away in the southern constellation Carina.

Adapted from information issued by NASA / ESA / Hubble Heritage Project (STScI / AURA) / M. Livio (STScI) / N. Smith (UCB).

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Puzzle of the “Green Pea” galaxies

"Green Pea" galaxies

A selection of "Green Pea" galaxies discovered by "citizen scientists" of the Galaxy Zoo team.

Galaxies come in many different shapes and sizes. There are spiral galaxies, like our Milky Way; elliptical types, like the Andromeda Galaxy, and irregular types, like the Small and Large Magellanic Clouds, visible to stargazers in the Southern Hemisphere.

But galaxies that look like green peas floating in space?

That’s exactly what a bunch of “citizen scientists” found in 2007, as part of a worldwide online effort to categories millions of galaxies photographed by a project called the Sloan Digital Sky Survey, or SDSS.

The SDSS had imaged the northern sky in great detail. But astronomers didn’t have a hope of categorising all the galaxies captured by the SDSS images—there just weren’t enough hours in the day.

So, through an online project called Galaxy Zoo (followed by Galaxy Zoo 2), they enlisted the aid of recreational astronomers around the world to sort through the vast depository of night sky images.

Categorising and counting galaxy types is both important to learn about the evolution of the Universe. But it can also be difficult because of the ambiguous shape of many of the galaxies.

"Green Pea" galaxies

Another bunch of Green Pea galaxies. Astronomers think their strange colour comes from a lack of heavy metals.

And so it was that in 2007, some of the citizen scientists spotted galaxies that just didn’t fit into any of the standard categories. They were small, round and green…hence the name, “Green Pea” galaxies.

Alerted to the enigmatic objects, professional turned their attention to them, and soon came up with an explanation.

The Green Peas appear to be compact, low-mass galaxies undergoing a brief burst of intense star formation. They also seem to be “metal-poor”…metals in this astronomical sense meaning any element heavier than hydrogen and helium.

It seems the heavier element gases have been either blasted out of the galaxies by “winds” produced by supernovae (exploding stars), or have been sucked out the gravitational pull of nearby galaxies. Maybe both explanations are right.

Astronomer Ricardo Amorin says, “This Green Pea discovery is a fabulous example of how normal citizens, ‘astronomy lovers’, can help scientists with their collective efforts.”

“Discovering Green Pea galaxies has opened a new window to investigate galaxy evolution and star formation in the early Universe.”

The latest incarnation of Galaxy Zoo uses data provided by the Hubble Space Telescope, to peer deeper into the Universe than before. Perhaps even more citizen science discoveries are just around the corner.

Adapted from information issued by JENAM / SDSS / Richard Nowell.

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More mini-Plutos found

Artist's concept of a TNO

Astronomers culling the data archives of NASA's Hubble Space Telescope have added 14 new distant icy worlds to the catalogue. The newfound trans-Neptunian Objects range from 40 to 100 km across. (Artist's concept)

  • Astronomers dig into Hubble image archives
  • Find 14 new mini-Plutos on Solar System’s edge
  • Range in size from 40 to 100 kilometres

Astronomers using clever techniques to cull the data archives of NASA’s Hubble Space Telescope have added 14 new distant icy worlds to the catalogue. Their method promises to turn up hundreds more.

Beyond the orbit of Neptune reside countless icy rocks known as trans-Neptunian objects (TNOs). One of the biggest, Pluto, is classified as a dwarf planet. The region also supplies us with comets such as famous Comet Halley. Most TNOs are small and receive little sunlight, making them faint and difficult to spot.

“Trans-Neptunian objects interest us because they are building blocks left over from the formation of the Solar System,” explained lead author Cesar Fuentes, formerly with the Harvard-Smithsonian Centre for Astrophysics and now at Northern Arizona University.

As TNOs slowly orbit the Sun, they move against the starry background, appearing as streaks of light in time exposure photographs. The team developed software to analyse hundreds of Hubble images hunting for such streaks.

After promising candidates were flagged, the images were visually examined to confirm or refute each discovery.

Most TNOs are located near the ecliptic—a line in the sky marking the plane of the Solar System. Therefore, the team searched within 5 degrees of the ecliptic to increase their chance of success.

They found 14 objects, including one binary (two TNOs orbiting each other like a miniature Pluto-Charon system). All were very faint, with most of them more than 100 million times fainter than can be seen with the unaided eye.

By measuring their motion across the sky, astronomers calculated an orbit and distance for each object. Combining the distance and brightness (plus an assumed albedo, or reflectivity), they then estimated the size. The newfound TNOs range from 40 to 100 kilometres (25 to 60 miles) across.

Artist's concept of Pluto and Charon

Artist's concept of the dwarf planet Pluto and its biggest moon, Charon. Both are considered to be trans-Neptunian Objects…icy worlds that live beyond the orbit of Neptune.

When worlds collide

Unlike planets, which tend to have very flat orbits (known as low inclination), some TNOs have orbits significantly tilted from the ecliptic (high inclination). The team examined the size distribution of TNOs with low- versus high-inclination orbits to gain clues about how the population has evolved over the past 4.5 billion years.

Generally, smaller trans-Neptunian objects are the shattered remains of bigger TNOs. Over billions of years, these objects crash together, grinding each other down. The team found that the size range of TNOs with low- versus high-inclination orbits is about the same as objects get fainter and smaller. Therefore, both populations (low and high inclination) have similar collisional histories.

This initial study examined only one-third of a square degree of the sky, meaning that there is much more area to survey. Hundreds of additional TNOs may lurk in the Hubble archives at higher ecliptic latitudes. Fuentes and his colleagues intend to continue their search.

“We have proven our ability to detect and characterise TNOs even with data intended for completely different purposes,” Fuentes said.

Adapted from information issued by Harvard-Smithsonian Centre for Astrophysics / NASA / ESA / G. Bacon (STScI) / ESO.

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Searching for stinky planets

Artist's conception of a volcanic moon

Artist's conception of an extremely volcanic moon orbiting a gas giant planet in another star system.

  • Exoplanet atmospheres can now be analysed
  • Super-volcanoes could emit copious sulphur gases
  • Could be detected by next generation space telescope

Astronomers think they’ve found a way to detect the presence of sulphur-spewing volcanoes on planets orbiting stars beyond our Solar System.

Volcanoes display the awesome power of Nature like few other events. Earlier this year, ash from an Icelandic volcano disrupted air travel throughout much of northern Europe. Yet this recent eruption pales next to the fury of Jupiter’s moon Io, the most volcanic body in our Solar System.

And now that astronomers are finding rocky worlds orbiting distant stars, they’re asking the next logical questions: Do any of those worlds have volcanoes? And if so, could we detect them?

Work by theorists at the Harvard-Smithsonian Centre for Astrophysics suggests that the answer to the latter is a qualified “Yes.”

“You would need something truly earthshaking, an eruption that dumped a lot of gases into the [planet’s] atmosphere,” said Smithsonian astronomer Lisa Kaltenegger.

“Using the James Webb Space Telescope, we could spot an eruption 10 to 100 times the size of Pinatubo for the closest stars,” she added.

Jupiter's moon Io

Jupiter's moon Io is the most volcanically active body in the Solar System.

Astronomers are decades away from being able to take images of the surface of alien worlds, or “exoplanets”. However, in a few cases they’ve been able to detect the atmospheres of “gas giant” planets known as “hot Jupiters.”

A volcanic eruption would emit fumes and various gases, so volcanic activity on a rocky exoplanet might leave a telltale chemical signature in the planet’s atmosphere.

Sniffing out volcanoes on other world

To work out which volcanic gases might be detectable, Kaltenegger and her Harvard colleagues, Wade Henning and Dimitar Sasselov, developed a computer model for eruptions on an Earth-like exoplanet based on the present-day Earth.

They found that sulphur dioxide from a very large, explosive eruption is potentially measurable because a lot is produced and it is slow to wash out of the air.

Sulphur dioxide has a sharp, acrid smell, sometimes described as similar to the smell of a just lit match.

To look for volcanic sulphur dioxide, astronomers would rely on a technique known as a secondary eclipse, when the exoplanet goes behind its star as seen from Earth.

By collecting light from the star and planet, then subtracting the light from the star alone (while the planet is hidden in the eclipse), astronomers are left with the light spectrum from just the planet. They can examine that spectrum for signs of particular chemical molecules.

Artist's concept of an exoplanet orbiting a star

Artist's concept of an exoplanet orbiting a star. By measuring the light both when the planet is in front of and behind (eclipse) by the star, astronomers can isolate the planet's light and gain information about it's atmospheric gases.

“Our first sniffs of volcanoes from an alien Earth might be pretty rank!” Kaltenegger said. “Seeing a volcanic eruption on an exoplanet will show us similarities or differences among rocky worlds.”

Catching one in the act

The 1991 eruption of Mount Pinatubo in the Philippines spewed about 17 million tonnes of sulphur dioxide into the stratosphere—a layer of air 10 to 45 miles above Earth’s surface. The largest volcanic eruption in recorded history, the 1815 Tambora event, was about 10 times more powerful.

Such gigantic eruptions are infrequent, so astronomers would have to monitor many rocky, Earth-sized exoplanets for years to catch one in the act. However, if alien worlds are more volcanically active than Earth, success might be more likely.

“A Tambora-sized eruption doesn’t happen often here, but could be more common on a younger planet, or a strongly tidally active planet—analogous to Io,” said Henning. “Once you detected one eruption, you could keep watch for further ones, to learn if frequent eruptions are common on other planets.”

Due to its proximity, a hypothetical Earth or super-Earth orbiting the nearby star Alpha Centauri would offer a best-case scenario for a sun-like star.

But any Earth-like planet less than 30 light-years away could show faint signs of volcanism when studied with the James Webb Space Telescope, the next generation optical telescope due to be launched in the middle of this decade.

Adapted from information issued by CfA / Wade Henning / NASA.

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Otherworldly artwork

Dust devil tracks on Mars

Tracks left by dust devils moving across the Martian dune plains.

These amazing patterns were spotted in the northern hemisphere of Mars on August 24, 2009 by the HiRISE camera aboard NASA’s orbiting Mars Reconnaissance Orbiter (MRO) spacecraft.

They are the tracks left by dust devils—mini tornadoes—moving across the Martian dunes.

Satellite image of a Martian dust devil

Looking down on a Martian dust devil...the small, round fuzz ball near the bottom left corner. The shadow cast by the devil can be seen to its left.

Take a look at the high-resolution version (will open in a new window or tab) of the image—it’s quite amazing.

Dust devils form when the Sun heats the surface so that the ground is warm to the touch, even though the atmosphere at 2 metres (6 feet) above the surface would be chilly. That temperature contrast causes convection (rising air) to where the wind speed is slightly higher. Mixing the dust, winds, and convection triggers the dust devils.

Scientists use images of dust devils to study several things. Tracking the devils shows which way the wind blows at different times of day. Statistics on the size of typical dust devils will help with estimates of how much dust they pump into the atmosphere every day. And by watching individual devils change as they go over more-dusty and less-dusty terrain, researchers can learn about the turbulent motion near the surface. Ultimately, that motion of wind and dust near the surface relates these small dust devils with Mars’ much larger dust storms.

MRO was 285 kilometres above the Martian surface at the time it took the image, which shows detail down to about 1.7 metres resolution.

The video below shows the progress of a dust devil moving across the plains in full view of the Spirit lander. The sequence of images spans a period of 9 minutes and 35 seconds, but has been speeded up for the purposes of the video.

Adapted from information issued by NASA / JPL-Caltech / Cornell University / Texas A&M / University of Arizona.

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