Confirmed: Earth’s “Martian meteorites” really are from Mars

PASADENA, Calif. — Examination of the Martian atmosphere by NASA’s Curiosity Mars rover confirms that some meteorites that have dropped to Earth really are from the Red Planet.

A key new measurement of the inert gas argon in Mars’ atmosphere by Curiosity’s laboratory provides the most definitive evidence yet of the origin of Mars meteorites while at the same time providing a way to rule out Martian origin of other meteorites.

The new measurement is a high-precision count of two forms of argon — argon-36 and argon-38 — accomplished by the Sample Analysis at Mars (SAM) instrument inside the rover. These lighter and heavier forms, or isotopes, of argon exist naturally throughout the solar system. On Mars the ratio of light to heavy argon is skewed because much of that planet’s original atmosphere was lost to space. The lighter form of argon was taken away more readily because it rises to the top of the atmosphere more easily and requires less energy to escape. That left the Martian atmosphere relatively enriched in the heavier isotope, argon-38.

Years of past analyses by Earth-bound scientists of gas bubbles trapped inside Martian meteorites had already narrowed the Martian argon ratio to between 3.6 and 4.5 (that is 3.6 to 4.5 atoms of argon-36 to every one of argon-38). Measurements by NASA’s Viking landers in the 1970s put the Martian atmospheric ratio in the range of four to seven. The new SAM direct measurement on Mars now pins down the correct argon ratio at 4.2.

“We really nailed it,” said Sushil Atreya of the University of Michigan, Ann Arbor, lead author of an Oct. 16 paper reporting the finding in Geophysical Research Letters. “This direct reading from Mars settles the case with all Martian meteorites.”

One reason scientists have been so interested in the argon ratio in Martian meteorites is that it was — before Curiosity — the best measure of how much atmosphere Mars has lost since the planet’s wetter, warmer days billions of years ago. Figuring out the planet’s atmospheric loss would enable scientists to better understand how Mars transformed from a once water-rich planet, more like our own, into today’s drier, colder and less-hospitable world.

Had Mars held onto all of its atmosphere and its original argon, its ratio of the gas would be the same as that of the sun and Jupiter. Those bodies have so much gravity that isotopes can’t preferentially escape, so their argon ratio — which is 5.5 — represents that of the primordial solar system.

While argon makes up only a tiny fraction of the gas lost to space from Mars, it is special because it’s a noble gas. That means the gas is inert, not reacting with other elements or compounds, and therefore a more straightforward tracer of the history of the Martian atmosphere.

“Other isotopes measured by SAM on Curiosity also support the loss of atmosphere, but none so directly as argon,” said Atreya. “Argon is the clearest signature of atmospheric loss because it’s chemically inert and does not interact or exchange with the Martian surface or the interior. This was a key measurement that we wanted to carry out on SAM.”

The Curiosity measurements do not directly measure the current rate of atmospheric escape, but NASA’s next mission to Mars, the Mars Atmosphere and Volatile Evolution Mission (MAVEN), is designed to do so. That mission is being prepared at NASA’s Kennedy Space Center in Florida for a launch-opportunity period that begins on Nov. 18.

Fireball thrills observers

Published on Sep 28, 2013
Last night, a meteor exploded in the skies above the US midwest. Witnesses report shadows cast upon the ground, unusual sounds, and a swirling contrail marking the aftermath of the blast. A NASA all-sky camera in Hiram, Ohio, recorded the fireball at 11:33 pm EDT: 

”This was a very bright event,” reported Bill Cooke of NASA’s Meteoroid Environment Office. “Flares saturated our meteor cameras, and made determination of the end point (the terminus of the fireball’s flight through the atmosphere) virtually impossible. Judging from the brightness, we are dealing with a meter-class object.”

Data from multiple cameras shows that the meteoroid hit Earth’s atmosphere traveling 51 km/s (114,000 mph) and passed almost directly over Columbus, Ohio. Cooke has prepared a preliminary map of the ground track. According to the American Meteor Society, the fireball was visible from at least 14 US states. The meteor is estimated to have exploded 41 miles directly above Columbus, Ohio.

Members of the CAA, at the club’s Letha House Park observing site near Spencer, Ohio, also saw the event. Observatory Director Jay Reynolds recounted the sight: “[Others] were observing in the parking lot, I was in the observatory reviewing photos I had taken when the observatory grew from darkness to BRIGHT in half a second! [It was] initially white, then green, then FLASH as if someone took a photo. As we looked, Capricorn now had a large glowing scar running 15-20 degrees horizontally across, running through it. The smoke trail was so bright, it too, may have been able to cast a shadow in the first second after it’s flashy birth, slowly fading, taking nearly a minute to disappear.”

February asteroids: A hit and a miss!

NASA Statement, 2/15/2013

New information provided by a worldwide network of sensors has allowed scientists to refine their estimates for the size of the object that entered that atmosphere and disintegrated in the skies over Chelyabinsk, Russia, at 7:20:26 p.m. PST, or 10:20:26 p.m. EST on Feb. 14 (3:20:26 UTC on Feb. 15).

The estimated size of the object, prior to entering Earth’s atmosphere, has been revised upward from 49 feet (15 meters) to 55 feet (17 meters), and its estimated mass has increased from 7,000 to 10,000 tons. Also, the estimate for energy released during the event has increased by 30 kilotons to nearly 500 kilotons of energy released. These new estimates were generated using new data that had been collected by five additional infrasound stations located around the world – the first recording of the event being in Alaska, over 6,500 kilometers away from Chelyabinsk. The infrasound data indicates that the event, from atmospheric entry to the meteor’s airborne disintegration took 32.5 seconds. The calculations using the infrasound data were performed by Peter Brown at the University of Western Ontario, Canada.

“We would expect an event of this magnitude to occur once every 100 years on average,” said Paul Chodas of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif. “When you have a fireball of this size we would expect a large number of meteorites to reach the surface and in this case there were probably some large ones.”

The trajectory of the Russia meteor was significantly different than the trajectory of the asteroid 2012 DA14, which hours later made its flyby of Earth, making it a completely unrelated object. The Russia meteor is the largest reported since 1908, when a meteor hit Tunguska, Siberia.


Bright fireball thrills Northern Ohioans

WOW! Did you see that?
If you were walking the dog last night about 9:55, you may have seen the BRIGHT meteor in the skies over Northern Ohio! Observers report a bright streak with green and blue in it, suggesting the presence of iron in the space rock. While not unexpected, this time of year, we are able to see what as known as the June Lyrid Meteor shower (June 14-16). The June Lyrids usually don’t produce many sightings. Local reports range from Willoughby Hills, Bedford, Solon, Avon Lake, as far South as Youngstown. Mark Johnson, from {WEWS TV 5} reports sightings from Michigan and Toronto. — Jay Reynolds


“Saw it very well here in Bay Village. Unlike any meteor I have seen. It was incredible.” –Trevor Braun