Today, NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission — sent to Mars to explore its upper atmosphere, ionosphere and interactions with the Sun and solar wind — celebrates 1,000 Earth days in orbit around the Red Planet.
This artist’s concept shows MAVEN in orbit around Mars, with a fanciful image of Earth in the background. Image credit: NASA / GSFC.
MAVEN, part of NASA’s Mars Scout program, launched on November 18, 2013, and successfully entered the orbit of the Red Planet on September 21, 2014.
The goal of the mission is to determine the role that loss of atmospheric gas to space played in changing the Martian climate through time. The spacecraft is studying the entire region from the top of the upper atmosphere all the way down to the lower atmosphere so that the connections between these regions can be understood.
“MAVEN has made tremendous discoveries about the Mars upper atmosphere and how it interacts with the Sun and the solar wind,” said MAVEN principal investigator Dr. Bruce Jakosky, from the University of Colorado, Boulder.
“These are allowing us to understand not just the behavior of the atmosphere today, but how the atmosphere has changed through time.”
“We’re excited that MAVEN is continuing its observations. It’s now observing a second Martian year, and looking at the ways that the seasonal cycles and the solar cycle affect the system,” said MAVEN project scientist Dr. Gina DiBraccio, from NASA’s Goddard Space Flight Center.
During its 1,000 days in orbit, MAVEN has made a multitude of stunning discoveries:
1. The Martian atmosphere has been stripped away by the Sun and the solar wind over time, changing the climate from a warmer and wetter environment early in history to the cold, dry climate that we see today.
2. MAVEN has measured the rate at which the Sun and the solar wind are stripping gas from the top of the atmosphere to space today, along with the details of the removal processes; extrapolation of the loss rates into the ancient past — when the solar ultraviolet light and the solar wind were more intense — indicates that large amounts of gas have been lost to space through time.
3. MAVEN has used measurements of light and heavy isotopes of the noble gas argon in the upper Martian atmosphere to determine how much gas has been lost through time; these measurements suggest that 65% of the atmospheric gas has been lost to space.
4. MAVEN made the first direct observations of a layer of metal (iron, magnesium and sodium) ions in the Martian electrically charged upper atmosphere (ionosphere), resulting from incoming interplanetary dust hitting the atmosphere; this layer is always present, but was enhanced by the close passage to Mars of Comet Siding Spring in October 2014.
5. MAVEN observed the full seasonal variation of hydrogen in the upper atmosphere, confirming that it varies by a factor of 10 throughout the year; the source of the hydrogen ultimately is water in the lower atmosphere, broken apart into hydrogen and oxygen by sunlight.
6. MAVEN has identified two new types of aurora, termed ‘diffuse’ and ‘proton’ aurora; unlike how we think of most aurorae on Earth, these aurorae are unrelated to either a global or local magnetic field.
7. These aurorae are caused by an influx of particles from the Sun ejected by different types of solar storms; when particles from these storms hit the Martian atmosphere, they also can increase the rate of loss of gas to space, by a factor of ten or more.
8. Imaging of the distribution of gaseous nitric oxide and ozone in the atmosphere shows complex behavior that was not expected, indicating that there are dynamical processes of exchange of gas between the lower and upper atmosphere that are not understood at present.
9. Some particles from the solar wind are able to penetrate unexpectedly deep into the upper atmosphere, rather than being diverted around the planet by the Martian ionosphere; this penetration is allowed by chemical reactions in the ionosphere that turn the charged particles of the solar wind into neutral atoms that are then able to penetrate deeply.
10. The interactions between Mars and the solar wind are unexpectedly complex; this results due to the lack of an intrinsic Martian magnetic field and the occurrence of small regions of magnetized crust that can affect the incoming solar wind on local and regional scales; the magnetosphere that results from the interactions varies on short timescales and is ‘lumpy’ as a result.
