[meteorite-list] Second Cycle of Martian Seasons Completing for Curiosity Rover

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=6512

Second Cycle of Martian Seasons Completing for Curiosity Rover
Jet Propulsion Laboratory
May 11, 2016

NASA's Curiosity Mars rover today completes its second Martian year since 
landing inside Gale Crater nearly four Earth years ago, which means it 
has recorded environmental patterns through two full cycles of Martian 
seasons.

The repetition helps distinguish seasonal effects from sporadic events. 
For example, a large spike in methane in the local atmosphere during the 
first southern-hemisphere autumn in Gale Crater was not repeated the second 
autumn. It was an episodic release, still unexplained. However, the rover's 
measurements do suggest that much subtler changes in the background methane 
concentration -- amounts much less than during the spike -- may follow 
a seasonal pattern. Measurements of temperature, pressure, ultraviolet 
light reaching the surface and the scant water vapor in the air at Gale 
Crater show strong, repeated seasonal changes.

Monitoring the modern atmosphere, weather and climate fulfills a Curiosity 
mission goal supplementing the better-known investigations of conditions 
billions of years ago. Back then, Gale Crater had lakes and groundwater 
that could have been good habitats for microbes, if Mars has ever had 
any. Today, though dry and much less hospitable, environmental factors 
are still dynamic.

Curiosity's Rover Environmental Monitoring Station (REMS), supplied by 
Spain's Centro de Astrobiología, has measured air temperatures from 60.5 
degrees Fahrenheit (15.9 degrees Celsius) on a summer afternoon, to minus 
148 F (minus 100 C) on a winter night. Seasonal patterns in temperature, 
water vapor and pressure that Curiosity has measured in Gale Crater are 
charted in a new graphic at:

http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA20600

"Curiosity's weather station has made measurements nearly every hour of 
every day, more than 34 million so far," said Curiosity Project Scientist 
Ashwin Vasavada of NASA's Jet Propulsion Laboratory, Pasadena, California. 
"The duration is important, because it's the second time through the seasons 
that lets us see repeated patterns."

Each Martian year -- the time it takes the Red Planet to orbit the sun 
once -- lasts 687 Earth days. Curiosity landed on Aug. 5, 2012, (Pacific 
Time; Aug. 6, Universal Time). It begins its third Martian year on May 
11, 2016, during the mission's 1,337th Martian day, or "sol," since landing. 
Each Martian sol lasts about 39.6 minutes longer than an Earth day, and 
a Martian year lasts 668.6 sols.

The similar tilts of Earth and Mars give both planets a yearly rhythm 
of seasons. But some differences are great, such as in comparisons between 
day and night temperatures. Even during the time of the Martian year when 
temperatures at Gale Crater rise above freezing during the day, they plummet 
overnight below minus 130 F (minus 90 C), due to the thin atmosphere. 
Also, the more-elliptical orbit of Mars, compared to Earth, exaggerates 
the southern-hemisphere seasons, making them dominant even at Gale Crater's 
near-equatorial location.

"Mars is much drier than our planet, and in particular Gale Crater, near 
the equator, is a very dry place on Mars," said Germán Martínez, a Curiosity 
science-team collaborator from Spain at the University of Michigan, Ann 
Arbor. "The water vapor content is a thousand to 10 thousand times less 
than on Earth."

Relative humidity is a function of both temperature and water-vapor content. 
During winter nights, Curiosity has measured relative humidity of up to 
70 percent, high enough to prompt researchers to check for frost forming 
on the ground. Other Mars landers have detected frost, but Curiosity has 
not.

Curiosity's air-pressure measurements confirm a strong seasonal trend 
previously seen by other missions. "There are large changes due to the 
capture and release of carbon dioxide by the seasonal polar caps," Martínez 
explained. Most of the Martian atmosphere is carbon dioxide. During each 
pole's winter, millions of tons of this gas freeze solid, only to be released 
again in spring, prompting very un-Earthlike seasonal variations of about 
25 percent in atmospheric pressure.

Other seasonal patterns measured by Curiosity and repeated in the rover's 
second Martian year are that the local atmosphere is clear in winter, 
dustier in spring and summer, and windy in autumn. Visibility in Gale 
Crater is as low as 20 miles (30 kilometers) in summer, and as high as 
80 miles (130 kilometers) in winter.

For tracking changes in the concentration of methane in the air above 
Gale Crater, researchers use the tunable laser spectrometer in Curiosity's 
Sample Analysis at Mars (SAM) suite of instruments. These measurements 
are made less often than REMS measurements, though frequently enough to 
tease out seasonal patterns. For most of the two Martian years, the rover 
has measured methane concentrations between 0.3 and 0.8 parts per billion. 
For several weeks during the first autumn, the level spiked, reaching 
7 parts per billion. The mission checked carefully for a repeat of that 
spike during the second autumn, but concentrations stayed at lower background 
levels.

"Doing a second year told us right away that the spike was not a seasonal 
effect," said JPL's Chris Webster of the SAM team. "It's apparently an 
episodic event that we may or may not ever see again."

However, the mission is continuing to monitor a possible seasonal pattern 
in the background methane concentration. The background level is far less 
than the spike level, but it appears to be even lower in autumn than in 
other seasons. If this pattern is confirmed, it may be related to the 
pressure pattern measured by REMS or to seasonal change in ultraviolet 
radiation, which is measured by REMS in concert with the rover's Mast 
Camera.

"This shows not only the importance of long-term monitoring, but also 
the importance of combining more than one type of measurement from a single 
platform," Webster said.

While continuing to study the modern local environment, Curiosity is investigating 
geological layers of lower Mount Sharp, inside Gale Crater, to increase 
understanding of ancient changes in environmental conditions. For more 
information about Curiosity, visit:

http://mars.jpl.nasa.gov/msl


News Media Contact

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster at jpl.nasa.gov 

Dwayne Brown / Laurie Cantillo
NASA Headquarters, Washington
202-358-1726 / 202-358-1077
dwayne.c.brown at nasa.gov / laura.l.cantillo at nasa.gov 

2016-128