Piling on to the good news from Mars this week, NASA’s MAVEN spacecraft sent home its first ultraviolet images from Mars. While they may not be flashy, these images will help determine the composition and variability of the upper atmosphere, and investigate the mystery of when the water escaped.
Top image: Ultraviolet composite image of the Martian atmosphere: blue hydrogen, green oxygen, and red planetary surface. Credit: NASA/University of Colorado
Maven’s Imaging Ultraviolet Spectrograph (IUVS) is the third ultraviolet imager to be mounted on a Mars orbiter, following after the Mariner 9 Ultraviolet Spectrometer and the Mars Express SPICAM. Unlike earlier UV spectrographs, Maven’s instrument has two resolution modes (6 kilometer vertical limb; 200 kilometer horizontal) and a beam-splitter sending middle-UV (180 to 340 nanometer wavelengths) and far-UV (110 to 190 nanometer wavelengths) light to different detectors.
The oh-so-sexy IUVS. Image credit: LASP/ Aref Nammari)
IUVS is capable of detecting ultraviolet wavelengths from 110 to 340 nanometers to within 0.5 to 1 nanometer resolution. It will be observing the current state of the Martian upper atmosphere and how it interacts with solar wind and ultraviolet radiation, tracking changes over time and hopefully helping scientists identify what processes control those changes.
The upper atmosphere of Mars: hydrogen at 121 nanometer wavelengths [blue, left]; oxygen at 130 nanometer wavelengths [green, middle-left]; sunlight reflecting from the Martian surface [red, middle-right]; and composite of all three phenomena using those ultraviolet wavelengths [right]. Image credit: NASA/University of Colorado
These images were taken from an altitude of 36,500 kilometers. The blue image on the far left measures atomic hydrogen gas as a cloud extending thousands of kilometers above the surface, out of the image frame. The green image on the middle-left uses a higher wavelength of ultraviolet light to detect oxygen, a smaller cloud hugging the planet more tightly as gravity pulls more strongly on the heavier molecule. Both gases are plentiful, byproducts of water and carbon dioxide breakdown processes within the atmosphere. The red image is sunlight directly reflecting from the planet’s surface, with the brighter oval indicative of either an ice cap or low-altitude clouds.
Tracking the spacial and temporal variation of these gases, along with carbon, nitrogen, carbon monoxide, carbon dioxide, and ionized carbon dioxide, will help scientists better understand what processes are driving the atmosphere’s composition. The particularly interesting part for the water history of the planet involves measuring the ratio between light water and heavy water — hydrogen (121.567 nm) and deuterium (121.533 nm). That’s a task requiring a high level of precision. It has been successfully accomplished for the lower atmosphere on Mars before, but never for the upper atmosphere where gas loss is actually taking place. Determining the loss rate for these gases will also be key in back-analyzing just how much water the red planet held in the distant past.