Posted on by Nancy Atkinson

New Images Reveal “Pure” Water Ice at Low Latitudes on Mars

MRO took these images of a fresh, 6-meter-wide (20-foot-wide) crater on Mars on Oct. 18, 2008, (left) and on Jan. 14, 2009. Credit: NASA/JPL-Caltech/University of Arizona

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Images of recent impact craters taken by the HiRISE Camera on the Mars Reconnaissance Orbiter have revealed sub-surface water ice halfway between the north pole and the equator on Mars. While the Phoenix lander imaged subsurface ice where the top layer of soil had been disturbed at the landing site near the north pole, these new images – taken in quick succession, detecting how the ice sublimated away — are the first to show evidence of water ice at much lower latitudes. Surprisingly, the white ice may be made from 99 percent pure water.

“We knew there was ice below the surface at high latitudes of Mars, but we find that it extends far closer to the equator than you would think, based on Mars’ climate today,” said Shane Byrne of the University of Arizona, a member of the High Resolution Imaging Science Experiment, or HiRISE camera.

“The other surprising discovery is that ice exposed at the bottom of these meteorite impact craters is so pure,” Byrne said. “The thinking before was that ice accumulates below the surface between soil grains, so there would be a 50-50 mix of dirt and ice. We were able to figure out, given how long it took that ice to fade from view, that the mixture is about one percent dirt and 99 percent ice.”

Scientists used several instruments on MRO to take a series of images, detecting and confirming highly pure, bright ice exposed in new craters, ranging from 1.5 feet to 8 feet deep, at five different Martian sites.

Earlier and later HiRISE images of a fresh meteorite crater 12 meters, or 40 feet, across located within Arcadia Planitia on Mars show how water ice excavated at the crater faded with time. The images, each 35 meters, or 115 feet across, were taken in November 2008 and January 2009. Credit: NASA/JPL-Caltech/University of Arizona
Earlier and later HiRISE images of a fresh meteorite crater 12 meters, or 40 feet, across located within Arcadia Planitia on Mars show how water ice excavated at the crater faded with time. The images, each 35 meters, or 115 feet across, were taken in November 2008 and January 2009. Credit: NASA/JPL-Caltech/University of Arizona

The images here were taken of the Arcadia Planitia region, located northwest of the Tharsis region in the northern lowlands, at 40-60° North and 150-180° West. The before and after HiRISE images show a fresh meteorite crater 12 meters, or 40 feet, and reveal how water ice excavated at the crater faded with time. The images, each 35 meters, or 115 feet across, were taken in November 2008 and January 2009.

The discovery of these “white” impact craters began in August 2008, the orbiter’s Context camera team examined their images for any dark spots or other changes that weren’t visible in earlier images of the same area. Meteorites usually leave dark marks when they crash into dust-covered Mars terrain.
The HiRISE team followed up in September 2008 by taking high-resolution images of the dark spots.

“We saw something very unusual when we followed up on the first of these impact craters,” Byrne said, “and that was this bright blue material poking up from the bottom of the crater. It looked a lot like water ice. And sure enough, when we started monitoring this material, it faded away like you’d expect water ice to fade, because water ice is unstable on Mars’ surface and turns directly into water vapor in the atmosphere.”

A few days later in September 2008, the orbiter’s “CRISM” team used their Compact Reconnaissance Imaging Spectrometer for Mars and got the spectral signature of water ice exposed in one of the impact craters, further clinching the discovery.

The HiRISE camera on NASA's Mars Reconnaissance Orbiter took this image of a new, 8-meter (26-foot)-diameter meteorite impact crater in the topographically flat, dark plains within Vastitas Borealis, Mars, on November 1, 2008. The crater was made sometime after Jan. 26, 2008. Bright water ice was excavated by, and now surrounds, the crater. This entire image is 50 meters (164 feet) across. Credit: NASA/JPL-Caltech/University of Arizona
The HiRISE camera on NASA's Mars Reconnaissance Orbiter took this image of a new, 8-meter (26-foot)-diameter meteorite impact crater in the topographically flat, dark plains within Vastitas Borealis, Mars, on November 1, 2008. The crater was made sometime after Jan. 26, 2008. Bright water ice was excavated by, and now surrounds, the crater. This entire image is 50 meters (164 feet) across. Credit: NASA/JPL-Caltech/University of Arizona

“All of this had to happen very quickly because 200 days after we first saw the ice, it was gone, it was the color of dirt,” Byrne said. “If we had taken HiRISE images just a few months later, we wouldn’t have noticed anything unusual. This discovery would have just passed us by.”

How far water ice extends toward the equator depends largely on how much water has been available in the Martian atmosphere in the recent past, Byrne said: “The ice is a relic of a more humid climate not very long ago, perhaps just several thousand years ago.”

This map shows five locations where fresh impact cratering has excavated water ice from just beneath the surface of Mars (sites 1 through 5) and the Viking Lander 2 landing site (VL2), in the context of color coding to indicate estimated depth to ice. Image Credit: NASA/JPL/University of Arizona
This map shows five locations where fresh impact cratering has excavated water ice from just beneath the surface of Mars (sites 1 through 5) and the Viking Lander 2 landing site (VL2), in the context of color coding to indicate estimated depth to ice. Image Credit: NASA/JPL/University of Arizona

While Phoenix’s discovery of sub-surface ice was not totally unexpected, finding highly pure ice far closer to the equator because of random meteor impacts was unexpected, he said.

There are several theories about how a layer of such pure ice could have formed beneath Mars surface. Byrne said he thinks that one of the most promising ideas is that this ice on Mars formed in the same way that pure ice lenses form beneath the surface of the Earth.

“That’s where you have very thin films of liquid water around ice grains and soil grains and they migrate around to form clear ice lenses on top of the ice table, even at temperatures well below zero. This process is called ‘frost heave’ on Earth, and it’s considered a nuisance in most places because it cracks up roads and tilts walls and destroys foundations of houses.

“But on Mars it would be of great interest if we could discover a process that involved liquid water in today’s climate, and not just in some of the warmest areas of the planet but in some of the coldest areas of the planet in the high latitude regions,” Byrne said.

Source: EurekAlert

Posted on by Nancy Atkinson

Why is Mars Red? New Study Offers Surprises

Should Mars really be black? Credit: NASA/Mars Simulation Laboratory

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Is Mars red due to rocks being rusted by the water that once flooded the red planet? And is the only explanation for the hematite found by Mars orbiters and studied by the Mars Exploration rovers is that water once was present in volumes on Mars? Not necessarily, says a new study. Research done by Dr. Jonathan Merrison at the Aarhus Mars Simulation Laboratory in Denmark shows that the red dust that covers Mars may be formed by ongoing grinding of surface rocks. Liquid water need not have played any significant role in the red dust formation process.

“Mars should really look black, between its white polar caps, because most of the rocks at mid-latitudes are basalt,” said Merrison. “For decades we assumed that the reddish regions on Mars are related to the water-rich early history of the planet and that, at least in some areas, water-bearing heavily oxidized iron minerals are present.”

Fine red dust covers Mars’s surface and is even present in Mars’s atmosphere, dominating the weather and sometimes becoming so thick that it plunges the planet into darkness. Even though dust is ubiquitous, we do not fully understand its physical, chemical and geological properties.

Merrison and his team have been working on getting accurate measurements of the composition and mineralogy of Mars in order to understand the structure and evolution of the near-surface environment and its interaction with the atmosphere, as well as in searching for potential habitats on Mars.

In their recent laboratory study, the scientists at the Mars Simulation Laboratory have pioneered a novel technique to simulate the sand transport on Mars. They hermetically sealed sand (quartz) t samples in glass flasks and mechanically “tumbled” them for several months, turning each flask ten million times. After gently tumbling pure quartz sand for seven months, almost 10% of the sand had been reduced to dust. When scientists added powdered magnetite, an iron oxide present in Martian basalt, to the flasks they were surprised to see it getting redder as the flasks were tumbled.

Colors map percentages of hematite in the surface materials in Meridiani Planum on Mars from 5 percent (aqua) to 25 percent (red). Opportunity landed within the black oval. MER scientists say the rocks there had once been drenched in water. Credit: NASA
Colors map percentages of hematite in the surface materials in Meridiani Planum on Mars from 5 percent (aqua) to 25 percent (red). Opportunity landed within the black oval. MER scientists say the rocks there had once been drenched in water. Credit: NASA

“Reddish-orange material deposits, which resemble mineral mantles known as desert varnish, started appearing on the tumbled flasks. Subsequent analysis of the flask material and dust has shown that the magnetite was transformed into the red mineral hematite, through a completely mechanical process without the presence of water at any stage of this process,” said Dr. Merrison.

The scientists suspect that, as the quartz sand grains are tumbled around they get quickly eroded and an alteration of minerals through contact ensues. How exactly this happens need to be further investigated through more experimental and analytical work. What is clear though is that the first experiments show that this process occurs not only in air but also in a dried carbon dioxide atmosphere, that is, in conditions that perfectly resemble those occurring on Mars. It may also imply that the reddish Martian dust is geologically recent.

Scientists worldwide, aided by new missions and improved instrumentation reaching the planet, will continue developing new improved computer models and Earth-bound simulators to try to pierce through the red planet’s mysteries.

“By simulating the conditions and developing accurate analogues of the Martian environment, we will certainly gain a deeper understanding of its dusty nature. In particular, developing better analogues of the Martian surface and atmosphere is vital in interpreting observations made on Mars by landers as well as pioneering the next generation of experiments to be flown,” said Dr Merrison.

Merrison presented his findings at the European Planetary Science Congress last week.

Source: Europlanet

Posted on by Nancy Atkinson

Phoenix’s Telltale Tells All About Winds and Weather on Mars

The Telltale instrument on the Phoenix lander. Credit: University of Aarhus.

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On board the plucky little Phoenix Mars lander was an even pluckier and littler device called the Telltale. It measured, for the first time, wind speeds and directions at the Mars polar region. Scientists have now been able to summarize the results from the Telltale, and presented their findings at the European Planetary Science Conference in Potsdam, Germany. They shared some unexpected new findings about the weather on Mars.

“Telltale has given us a wealth of information about the local Martian wind velocities and directions. At the Phoenix landing site, we were able to see meteorological changes caused by interactions between the dynamic north pole, where there are ever changing evaporation processes, and the Martian atmosphere,” said Dr. Haraldur Gunnlaugsson.

Artists rendition of Phoenix on Mars. Credit: NASA/JPL
Artists rendition of Phoenix on Mars. Credit: NASA/JPL

As you recall, Phoenix landed in the North polar region of Mars on May 25, 2008 and operated successfully for about 5 Earth months, or 151 Martian sols. The Telltale device consisted of a lightweight tube suspended on top of a meteorological mast, roughly two meters above the local surface. The device had to be sensitive enough to detect very light breezes, but also be able to withstand the violent vibrations during the mission launch. After landing on Mars, Phoenix’s onboard camera continuously imaged the deflection of the tube in the wind, taking more than 7,500 images during the mission.

The astronomers/meteorologists found the wind speeds and directions varied as the seasons changed. Easterly winds of approximately 15-20 kilometers per hour prevailed during the Martian mid-summer, but when autumn approached, the winds increased and switched to come predominantly from the West. While these winds appeared to be dominated by turbulence, the highest wind speeds recorded of up to nearly 60 kilometers per hour coincided with the passing of weather systems, when also the number of dust devils increased by an order of magnitude.

Mars is typically a rather windy place and learning more about the planet’s climatic conditions will contribute to the understanding of the Martian water cycle and the identification of areas on the red planet that could sustain life. Local wind measurements by the Telltale instrument, amended with daily images of the whole northern hemisphere by the Mars Reconnaissance Orbiter spacecraft, have allowed astronomers to gain much deeper information on weather systems on Mars.

“We’ve seen some unexpected night-time temperature fluctuations and are starting to understand the possible ways dust is put into suspension in the Martian atmosphere. For example, we could see that some of the dust storms on Mars do not require the existence of high winds,” said Dr Gunnlaugsson.

Source: Europlanet

Posted on by Jerry Coffey

When Was Mars Discovered?

This full-circle view from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Spirit shows the terrain surrounding the location called "Troy," where Spirit became embedded in soft soil during the spring of 2009. Credit: NASA/JPL

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It is impossible to know the answer to ”when was Mars discovered”. It is bright enough to be seen in the night sky without binoculars or a telescope and has been documented for at least 4,000 years.

If you were to change the question a little to ”who first theorized that Mars was a planet”, then an answer can be found. Nicolaus Copernicus is the first astronomer to postulate that Mars and a few other bodies known at the time were planets. The heliocentric theory that he published in 1543 marked the first time that astronomers widely considered the possibility that the Sun was the center of the Solar System instead of the Earth.

While no one knows who first discovered Mars, we do know who made many of the discoveries about the planet. It is known that Tycho Brahe, a Danish astronomer made accurate calculations of the position of Mars as early as 1576. Johannes Kepler theorized that the orbit of Mars was elliptical in contradiction to what astronomers believed at the time. He soon expanded that theory to encompass all planets. In 1659, Christian Huygens, a Dutch astronomer drew Mars with the observations he made using a telescope he designed himself. He also discovered a strange feature on the planet that became known as Syrtis Major.

On November 28, 1964, Mariner 4 was launched successfully on an eight-month voyage to the Red Planet. It made its first flyby on July 14, 1965, collecting the first close-up photographs of another planet. The pictures showed many impact craters, some of them touched with frost in the chill Martian evening. The Mariner 4 spacecraft was able to function for about three years in solar orbit, continuing long-term studies of the solar wind environment and making coordinated measurements with Mariner 5.

There are currently six spacecraft in orbit around Mars or on its surface and several more are in the planning or design stages. Five are gathering data at an amazing rate, the other(Phoenix) is non-functioning. New discoveries like subsurface water ice and methane plumes in the atmosphere are being made on a regular basis. Scientists may not be able to give an answer to ”when was Mars discovered”, but they can offer answers to thousands of other questions and the list is growing as we speak.

We have written many articles about the study of Mars. Here an article about how methane is being produced on Mars, and the possible discovery of life on Mars.

Here are some additional articles about the early observations of Mars, and here’s a whole book about observing Mars.

We have recorded an entire episode of Astronomy Cast about the planet Mars. Listen to it here, Episode 52: Mars.

Source: NASA

Posted on by Nancy Atkinson

After Loss of Lunar Orbiter, India Looks to Mars Mission

India Moon Mission
Artist concept of Chandrayaan-1 orbiting the moon. Credit: ISRO

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After giving up on re-establishing contact with the Chandrayaan-1 lunar orbiter, Indian Space Research Organization (ISRO) Chairman G. Madhavan Nair announced the space agency hopes to launch its first mission to Mars sometime between 2013 and 2015. Nair said the termination of Chandrayaan-1, although sad, is not a setback and India will move ahead with its plans for the Chandrayaan-2 mission to land an unmanned rover on the moon’s surface to prospect for chemicals, and in four to six years launch a robotic mission to Mars.


“We have given a call for proposal to different scientific communities,” Nair told reporters. “Depending on the type of experiments they propose, we will be able to plan the mission. The mission is at conceptual stage and will be taken up after Chandrayaan-2.”

On the decision to quickly pull the plug on Chandrayaan-1, Nair said, “There was no possibility of retrieving it. (But) it was a great success. We could collect a large volume of data, including more than 70,000 images of the moon. In that sense, 95 percent of the objective was completed.”

Contact with Chandrayaan-1 may have been lost because its antenna rotated out of direct contact with Earth, ISRO officials said. Earlier this year, the spacecraft lost both its primary and back-up star sensors, which use the positions of stars to orient the spacecraft.

The loss of Chandrayaan-1 comes less than a week after the spacecraft’s orbit was adjusted to team up with NASA’s Lunar Reconnaissance Orbiter for a Bi-static radar experiment. During the maneuver, Chandrayaan-1 fired its radar beam into Erlanger Crater on the moon’s north pole. Both spacecraft listened for echoes that might indicate the presence of water ice – a precious resource for future lunar explorers. The results of that experiment have not yet been released.

Chandrayaan-1 craft was designed to orbit the moon for two years, but lasted 315 days. It will take about 1,000 days until it crashes to the lunar surface and is being tracked by the U.S. and Russia, ISRO said.

The Chandrayaan I had 11 payloads, including a terrain-mapping camera designed to create a three-dimensional atlas of the moon. It is also carrying mapping instruments for the European Space Agency, radiation-measuring equipment for the Bulgarian Academy of Sciences and two devices for NASA, including the radar instrument to assess mineral composition and look for ice deposits. India launched its first rocket in 1963 and first satellite in 1975. The country’s satellite program is one of the largest communication systems in the world.

Sources: New Scientist, Xinhuanet

Posted on by Nancy Atkinson

Future Designs: Robotic Mars Greenhouse, Teleporting Fridge

"Little Prince" robot greenhouse. Credit: Electrolux

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Now THIS is what I’m talking about! Every year Electrolux holds a competition for students to design concepts for future appliances, and they’ve just announced the eight finalists. My favs: a robotic greenhouse for Mars and a teleporting refrigerator. Le Petit Prince (Little Prince) is a robotic greenhouse concept that is specially designed to help the future exploration and expanding population when we colonize Mars. This intelligent robot carries and cares for a plant inside its glass container, which is functionally mounted on a four-legged self-transporting pod. Not only does it search for the optimum place to receive enough sunlight and other nutrients, it also send reports of its movements and developments to its fellow greenhouse robots through wireless communication. It was designed by Martin Miklica, from the Brno University of Technology in the Czech Republic. He said he was inspired by the book The Naked Sun by Isaac Asimov and R2-D2 from Star Wars (and surely Wall-E had something to do with this, too.)

See video of Le Petit Prince, below, and of the teleporting fridge.

This one I can’t wait for: The Teleport Fridge by Dulyawat Wongnawa, Chulalongkorn University, Thailand. Once we figure out how to beam things up, the Teleport Fridge teleports food, eliminating the time and distance a person has to travel to buy fresh groceries or products from a store or farm. Using touch-screen technology as the interface for the teleportation process, the Teleport Fridge simply teleports food to compartments in its refrigeration and freezer units. If the food spoils, it teleports it to the compost pile. Very cool, but it takes the adventure out of opening those containers in the back of the fridge.

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See the other six design concepts and vote for your favorite here.

Source: Electrolux Design Lab

Posted on by Nancy Atkinson

Mars Reconnissance Orbiter Goes Into Safe Mode Again

Artists concept of the Mars Reconnaisance Orbiter. Credit: NASA/JPL

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NASA’s Mars Reconnaissance Orbiter put itself into a safe mode Wednesday morning, Aug. 26, for the fourth time this year. While in safe mode, the spacecraft can communicate normally with Earth, but aborts its scheduled activities, and awaits further instructions from ground controllers. “We hope to gain a better understanding of what is triggering these events and then have the spacecraft safely resume its study of Mars by next week,” said MRO Project Manager Jim Erickson.

Engineers have begun the process of diagnosing the problem prior to restoring the orbiter to normal science operations, a process expected to take several days. They will watch for engineering data from the spacecraft that might aid in identifying the cause of event and possibly of previous ones.

A possible cause for the frequent anomalies is cosmic ray hits. But the spacecraft has reacted differently with the various safe mode entries. The orbiter spontaneously rebooted its computer Wednesday, as it did in February and June, but did not switch to a redundant computer, as it did in early August.

To help in investigating a root cause of the three previous anomalies, engineers had programmed the spacecraft to frequently record engineering data onto non-volatile memory. That could give an improved record of spacecraft events leading up to the reboot.

MRO has been in Mars orbit since 2006, and has returned more data than all other current and past Mars missions combined.

Source: JPL

Posted on by Abby Cessna

Solar System Orbits

Take a look at the Solar System from above, and you can see that the planets make nice circular orbits around the Sun. But dwarf planet’s Pluto’s orbit is very different. It’s highly elliptical, traveling around the Sun in a squashed circle. And Pluto’s orbit is highly inclined, traveling at an angle of 17-degrees. This strange orbit gives Pluto some unusual characteristics, sometimes bringing it within the orbit of Neptune. Credit: NASA

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One of the International Astronomical Union’s (IAU) requirements for a celestial body to be classified as a planet (or a dwarf planet) is that it orbits the Sun. All of the planets have different orbits, which affect many of the planets’ other characteristics.

Since Pluto became a dwarf planet, Mercury is the planet with the most eccentric orbit. The eccentricity of an orbit is the measurement of how different the orbit is from a circular shape. If an orbit is a perfect circle, its eccentricity is zero. As the orbit becomes more elliptical, the eccentricity increases. Mercury’s orbit ranges from 46 million kilometers from the Sun to 70 million kilometers from the Sun.

Venus, which is right next to Mercury, has the least eccentric orbit of any of the planet in the Solar System. Its orbit ranges between 107 million km and 109 million km from the Sun and has an eccentricity of .007 giving it a nearly perfect circle for its orbit.

Earth also has a relatively circular orbit with an eccentricity of .017. Earth has a perihelion of 147 million kilometers; the perihelion is the closest point to the Sun in an object’s orbit. Our planet has an aphelion of 152 million kilometers. An aphelion is the furthest point from the Sun in an object’s orbit.

Mars has one of the most eccentric orbits in our Solar System at .093. Its perihelion is 207 million kilometers, and it has an aphelion of 249 million kilometers.

Jupiter has a perihelion of 741 million kilometers and an aphelion of 778 million kilometers. Its eccentricity is .048. Jupiter takes 11.86 years to orbit the Sun. Although this seems a long time compared to the time our own planet takes to orbit, it is only a fraction of the time of some of the other planets’ orbits.

Saturn is 1.35 billion kilometers at its perihelion and 1.51 billion kilometers from the Sun at its furthest point. It has an eccentricity of .056. Since it was first discovered in 1610, Saturn has only orbited the Sun 13 times because it takes 29.7 years to orbit once.

Uranus is 2.75 billion miles from the Sun at its closest point and 3 billion miles from the Sun at its aphelion. It has an eccentricity of .047 and takes 84.3 years to orbit the Sun. Uranus has such an extreme axial tilt (97.8°) that rotates on its side. This causes radical changes in seasons.

Neptune is the furthest planet from the Sun with a perihelion of 4.45 billion kilometers and an aphelion of 4.55 billion kilometers. It has an eccentricity of .009, which is almost as low as Venus’ eccentricity. It takes Neptune 164.8 years to orbit the Sun.

Universe Today has articles on orbits of the planets and asteroid orbits.

For more information, check out articles on an overview of the Solar System and new planet orbits backwards.

Astronomy Cast has episodes on all the planets including Mercury.

References:
NASA: Transits of Mercury
NASA: Solar System Math
NASA: Mars, You’re So Complicated
NASA Solar System Exploration

Posted on by Nancy Atkinson

Watching Science in Action on Mars

This view of a rock called "Block Island," the largest meteorite yet found on Mars, comes from the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity. Credit: NASA/JPL

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One of the great things about the Mars Exploration Rovers is that we get to see these scrappy little vehicles ramble across the surface of Mars, and watch science in action. Case in point: the meteorite found by Opportunity, dubbed “Block Island.” Scientists are debating all sorts of things about this watermelon-sized rock. How old is it? What is it made of? Where could it have come from? But not only are we learning about this alien rock, we’re also learning about the Red Planet itself and its environmental history.

See below for a new 3-D version of Block Island created by Stu Atkinson.

3-D Block Island created by Stuart Atkinson.
3-D Block Island created by Stuart Atkinson.

Scientists calculate Block Island is too massive to have hit the ground without disintegrating unless Mars had a much thicker atmosphere than it has now when the rock fell. An atmosphere slows the descent of meteorites, and with today’s thin Martian atmosphere, this heavy rock would have plummeted to the surface.

Block Island is approximately 60 centimeters (2 feet) in length, half that in height, probably weighs about a half ton, and has a bluish tint that distinguishes it from other rocks in the area.

Opportunity found a smaller iron-nickel meteorite, called “Heat Shield Rock,” in late 2004. Block Island is roughly 10 times as massive as Heat Shield Rock and several times too big to have landed intact without more braking than today’s Martian atmosphere could provide.

“Consideration of existing model results indicates a meteorite this size requires a thicker atmosphere,” said rover team member Matt Golombek of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Either Mars has hidden reserves of carbon-dioxide ice that can supply large amounts of carbon-dioxide gas into the atmosphere during warm periods of more recent climate cycles, or Block Island fell billions of years ago.”

Additional studies also may provide clues about how weathering has affected the rock since it fell.

“There’s no question that it is an iron-nickel meteorite,” said Ralf Gellert of the University of Guelph in Ontario, Canada. Gellert is the lead scientist for the rover’s alpha particle X-ray spectrometer, an instrument on the arm used for identifying key elements in an object. “We already investigated several spots that showed elemental variations on the surface. This might tell us if and how the metal was altered since it landed on Mars.”

The triangular pattern of small ridges seen at the upper right in this image and elsewhere on the rock is characteristic of iron-nickel meteorites found on Earth, especially after they have been cut, polished and etched.
The triangular pattern of small ridges seen at the upper right in this image and elsewhere on the rock is characteristic of iron-nickel meteorites found on Earth, especially after they have been cut, polished and etched.

The microscopic imager on the arm revealed a distinctive triangular pattern in Block Island’s surface texture, matching a pattern common in iron-nickel meteorites found on Earth.

“Normally this pattern is exposed when the meteorite is cut, polished and etched with acid,” said Tim McCoy, a rover team member from the Smithsonian Institution in Washington. “Sometimes it shows up on the surface of meteorites that have been eroded by windblown sand in deserts, and that appears to be what we see with Block Island.”

Spectrometer observations have already identified variations in the composition of Block Island at different points on the rock’s surface. The differences could result from interaction of the rock with the Martian environment, where the metal becomes more rusted from weathering with longer exposures to water vapor or liquid.

“We have lots of iron-nickel meteorites on Earth. We’re using this meteorite as a way to study Mars,” said Albert Yen, a rover team member at JPL. “Before we drive away from Block Island, we intend to examine more targets on this rock where the images show variations in color and texture. We’re looking to see how extensively the rock surface has been altered, which helps us understand the history of the Martian climate since it fell.”

When the investigation of Block Island concludes, the team plans to resume driving Opportunity on a route from Victoria Crater, which the rover explored for two years, toward the much larger Endeavour Crater. Opportunity has covered about one-fifth of the 19-kilometer (12-mile) route plotted for safe travel to Endeavour since the rover left Victoria nearly a year ago.

Source: JPL

Posted on by Abby Cessna

Radius of the Planets

Size of the planets compared.

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One way to measure the size of the planets is by radius. Radius is the measurement from the center of an object to the edge of it.

Mercury is the smallest planet with a radius of only 2,440 km at its equator. Mercury is not that much larger than the Moon, and it is actually smaller than some of our Solar System’s larger satellites, such as Titan. Despite Mercury’s small size, it is actually dense with higher gravity than you would expect for its size.

Venus has a radius of 6,052 kilometers, which is only a few hundred kilometers smaller than Earth’s radius. Most planets have a radius that is different at the equator than it is at the poles because the planets spin so fast that they flatten out at the poles. Venus has the same diameter at the poles and at the equator though because it spins so slowly.

Earth is the largest of the four inner planets with a radius of 6,378 kilometers at the equator. This is over two times larger than the radius of Mercury. The radius between the poles is 21.3 km less than the radius at the equator because the planet has flattened slightly since it only takes 24 hours to rotate.

Mars is a surprisingly small planet with a radius of 3,396 kilometers at the equator and 3,376 kilometers at the poles. This means that Mars’ radius is only about half of Earth’s radius.

Jupiter is the largest of all the planets. It has a radius of 71,492 kilometers at the equator and a radius of 66,854 kilometers at the poles. This is a difference of 4,638 kilometers, which is almost twice Mercury’s radius. Jupiter has a radius at the equator 11.2 times Earth’s equatorial radius.

Saturn has an equatorial radius of 60,268 kilometers and a radius of 54,364 kilometers at the poles making it the second largest planet in our Solar System. The difference between its two radiuses is a little more than twice the radius of Mercury.

Uranus has an equatorial radius of 25,559 kilometers and a radius of 24,973 kilometers at the poles. Although this is much smaller than Jupiter’s radius, it is around four times the size of Earth’s radius.

Neptune’s equatorial radius of 24,764 kilometers makes it the smallest of the four outer planets. The planet has a radius of 24,341 kilometers at the poles. Neptune’s radius is almost four times the size of Earth’s radius, but it is only about a third of Jupiter’s radius.

Universe Today has articles on the radius of Neptune and the size of the planets.

If you are looking for more information, check out NASA’s Solar System exploration page, and here’s a link to NASA’s Solar System Simulator.

Astronomy Cast has an episode on Venus and more on all the planets.