[meteorite-list] Phoenix Mars Lander Finds Surprises About Planet's Watery Past

[Ron Baalke]

FOR IMMEDIATE RELEASE

FROM THE UNIVERSITY OF ARIZONA

Sept. 09, 2010

This story and photos are online at: http://uanews.org/node/34019

Contact information follows this story.

Phoenix Mars Lander Finds Surprises About Planet's Watery Past

An instrument designed and built at the UA measured the isotopic 
composition of the Mars atmosphere, suggesting liquid water has 
interacted with the Martian surface throughout the planet's history.
Liquid water has interacted with the Martian surface throughout Mars' 
history, measurements by NASA's Phoenix Mars Lander suggest.

The findings, published in the Sept. 10 issue of the journal Science, 
also suggest that liquid water has primarily existed at temperatures 
near freezing, implying hydrothermal systems similar to Yellowstone's 
hot springs on Earth have been rare on Mars throughout its history.

These surprising results come from measurements Phoenix made in 2008 
of stable isotopes of carbon and oxygen in the carbon dioxide of the 
Martian atmosphere. Isotopes are variants of the same element with a 
different number of neutrons, such as carbon-12, with six neutrons, 
and the rarer carbon-13, with seven.

Unprecedented precision in determining the ratios of isotopes in 
Martian carbon dioxide sheds new light on the history of water and 
volcanic activity on the surface of Mars.

The measurements were performed by the Evolved Gas Analyzer on 
Phoenix, part of the lander's Thermal and Evolved Gas Analyzer, or 
TEGA, an instrument designed and built at the University of Arizona. 
TEGA's mass spectrometer was capable of a more accurate analysis of 
carbon dioxide than the ones on NASA's Viking landers in the 1970s, 
the only other such instruments that have returned results on isotopic 
composition from Mars.

"We use the TEGA instrument as a crime scene investigator," said 
William V. Boynton, a professor at the Lunar and Planetary Lab in the 
UA's department of planetary sciences. "Like a chemical fingerprint, 
isotopes tell us what process is responsible for making the material 
we are studying." Boynton, who heads the group that built the TEGA 
instrument, co-authored the Science paper.

Carbon dioxide makes up about 95 percent of the Martian atmosphere. 
NASA's Mars Exploration Program has put a high priority on learning 
more about the isotope ratios in Martian carbon dioxide to supplement 
the information from Viking and from analysis of meteorites that have 
reached Earth from Mars.

For the measurement, the TEGA instrument on the lander opened a pin-
point-sized hole while a vacuum sucked a puff of Martian atmosphere 
into its chamber for isotope analysis.

The analysis revealed that carbon dioxide on Mars has proportions of 
carbon and oxygen isotopes similar to carbon dioxide in Earth's 
atmosphere. This unexpected result reveals that Mars is a much more 
geologically active planet than previously thought. In fact, the new 
results suggest that Mars has replenished its atmospheric carbon 
dioxide relatively recently, and that the carbon dioxide has reacted 
with liquid water present on the surface.

"Atmospheric carbon dioxide is like a chemical spy," said Paul Niles, 
a space scientist at NASA's Johnson Space Center in Houston and lead 
author of the paper. "It infiltrates every part of the surface of Mars 
and can indicate the presence of water and its history."

The low gravity and lack of a magnetic field on Mars mean that as 
carbon dioxide resides in the atmosphere it will be lost to space, a 
process that favors loss of the lighter carbon-12 isotope compared to 
carbon-13. Although an older atmosphere on Mars should contain much 
more carbon-13, it doesn't. This suggests that the Martian atmosphere 
has been recently replenished with carbon dioxide emitted from 
volcanoes, and volcanism has been an active process in Mars' 
geologically recent past.

Another clue comes from the second element that makes up carbon 
dioxide: oxygen. Oxygen, like carbon, comes in different isotopes: 
oxygen-16 and the heavier oxygen-18.

The team compared the results from Phoenix to measurements obtained 
from Martian meteorites that were hurled into space from the Red 
Planet's surface during impact events and eventually fell onto Earth 
where they were later collected. The meteorites contain carbonate 
minerals that form only in the presence of liquid water and carbon 
dioxide.

"Carbon dioxide spewed into the atmosphere by volcanoes is very 
similar in its oxygen isotope ratio to that found in rocks," said 
Boynton. "But we see a big difference between the oxygen ratios of the 
volcanic rocks and the atmosphere."

This suggests that the carbon dioxide in the volcanic rock of Martian 
meteorites has reacted with liquid water, enriching the oxygen in 
carbon dioxide with heavier oxygen-18.

The comparisons of isotopes in Mars' atmosphere with those in the 
meteorites provide confirmation of key findings. For example, one 
meteorite that crystallized during recent geological time on Mars - 
about 170 million years ago rather than billions of years ago - has 
carbonates with isotopic proportions that match the atmospheric 
measurements by Phoenix.

According to Niles, the isotopic signature indicates that liquid water 
has been present on the Martian surface recently and abundantly enough 
to affect the composition of the current atmosphere. It also reveals 
the water has primarily existed at temperatures near its freezing point.
The results provide supporting evidence that the watery conditions 
associated with carbonate formation have continued even under Mars' 
current cold and dry conditions.

"This shows that the carbonates formed under the influence of water 
and the atmosphere in the recent geologic past," Boynton said.
Niles added: "The findings do not reveal specific locations or dates 
of liquid water and volcanic vents, but geologically recent 
occurrences of those conditions provide the best explanations for the 
isotope proportions we found."

The University of Arizona conceived of and ran the Phoenix mission, 
which landed near the north pole of Mars in May of 2008; it is the 
first Mars mission ever led by a university. The Principal 
Investigator is Peter H. Smith, a professor at the UA's Lunar and 
Planetary Lab. NASA's Jet Propulsion Laboratory in Pasadena, Calif., 
provided the management of the project. For his leadership on the TEGA 
project, Boynton was recently honored with NASA's Exceptional Public 
Service Medal.

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CONTACTS:

William V. Boynton,
Lunar and Planetary Laboratory, The University of Arizona, (520) 
621-6941; wboynton at lpl.arizona.edu

Daniel Stolte, University of Arizona Office of Communications, (520) 
626-4402; stolte at email.arizona.edu