EXI Multispectral Image of Mars, showing volcanoes poking through the cloud layer
On 18 July 2021, the EXI camera system onboard the Hope probe obtained a set of multispectral images of a fully-illuminated hemisphere of Mars – which looks very similar to observations routinely carried out by weather satellites orbiting Earth. At the time the images were taken, the Hope spacecraft was at an altitude of about 20,260 kilometers above the surface; with the view centered at 11.0°N latitude, -79.4°E longitude, North is toward the top. In terms of the Martian season, it was late spring in the northern hemisphere.
Multispectral images (obtained at multiple wavelengths) are very useful when investigating details of planetary surfaces and atmospheres. Shorter wavelengths (blue and ultraviolet images) emphasize atmospheric features (clouds and hazes) while longer wavelengths (red images) emphasize surface features such as bright and dark surface markings. For example, in the EXI 635 nanometer (red) image presented here, surface features are very distinct while atmospheric hazes and clouds are quite subtle; in the EXI 320 nanometer (ultraviolet) image, the Martian surface is dark but atmospheric water-ice clouds and hazes are bright and distinct. By combining the individual images into a single colour image, one can view the notable surface and atmospheric features at the same time. This colour composite was assembled from images taken through EXI’s blue, green, and red filters (437, 546, and 635 nanometers) overlaid with an ultraviolet image (320 nanometers). These images have been “calibrated” to remove several types of artefacts introduced by the camera system. The contrast has been adjusted to enhance the visibility of surface and atmospheric features.
It is late spring in the northern hemisphere, the time of year when Mars reaches the maximum distance from the Sun (aphelion) in its elliptical orbit. This is also when atmospheric temperatures reach their minimum for the year, leading to widespread condensation of atmospheric water vapor and the formation of a band of water-ice clouds between the equator and about 30°N latitude. This so-called Aphelion Cloud Belt (ACB) is very distinct in the 320 nanometer and colour-composite images. Below the center in these images, the Valles Marineris canyon system stretches nearly 4000 kilometers across the surface. To the west, the upper slopes and summits of the massive Tharsis Montes volcanoes extend up through the clouds, forming four “dark spots”. The leftmost of these – Olympus Mons – at 600 km across and nearly 22 km tall, is the largest known mountain in the Solar System.
EMUS 130.4 nm – Dramatic variation in concentrations of Atomic Oxygen on Mars
This observation from the EMUS instrument (Emirates Mars Ultraviolet Spectrometer) was acquired on 24 April 2021 and shows vast structures in the airglow emitted by atomic oxygen from the dayside of Mars at a wavelength of 130.4 nm. This oxygen is produced when sunlight splits carbon dioxide molecules in the upper atmosphere at altitudes above 100 km. These measurements show higher than expected variations in the density of atomic oxygen and point to unusual levels of atmospheric turbulence.
One of three instruments on board the Mars Hope Probe, EMUS’ principal science goal is the measurement of oxygen and carbon monoxide in Mars’ upper atmosphere and the variability of hydrogen and oxygen in the exosphere. EMUS (Emirates Mars Ultraviolet Spectrometer) is the most sensitive ultraviolet instrument yet to orbit Mars.
EMUS 137-150 nm – Equally dramatic dayside variations in carbon monoxide
This observation from the EMUS instrument (Emirates Mars Ultraviolet Spectrometer) was acquired on 24 April 2021 and shows vast structures in the airglow emitted by carbon monoxide from the dayside of Mars at wavelengths of 137-150 nm. Along with atomic oxygen, this carbon monoxide (CO) is produced when sunlight splits carbon dioxide (CO2) in the upper atmosphere of Mars. Understanding the chemistry of carbon monoxide in the Martian atmosphere is a long-standing problem in planetary science, and these observations by EMM promise new avenues for progress.Email This Post