The Atmospheric Chemistry Suite (ACS) is a science payload consisting of three
infrared spectrometer
Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functio ...
channels aboard the
ExoMars Trace Gas Orbiter
The ExoMars Trace Gas Orbiter (TGO or ExoMars Orbiter) is a collaborative project between the European Space Agency (ESA) and the Russian Roscosmos agency that sent an atmospheric research orbiter and the ''Schiaparelli'' demonstration lande ...
(TGO) orbiting Mars since October 2016.
[''Three infrared spectrometers, an atmospheric chemistry suite for the ExoMars 2016 Trace Gas Orbiter''. Korablev, O., et al., 2014. J. Appl. Remote Sensing. 8, 4983.] The three channels are: the near-infrared channel (
NIR), the mid-infrared channel (MIR), and the far infrared channel (FIR, also called TIRVIM).
The ACS was proposed in 2011 by Russian Academy Section and eventually accepted by the
European Space Agency
The European Space Agency (ESA) is a 23-member International organization, international organization devoted to space exploration. With its headquarters in Paris and a staff of around 2,547 people globally as of 2023, ESA was founded in 1975 ...
(ESA) and
Roscosmos
The State Corporation for Space Activities "Roscosmos", commonly known simply as Roscosmos (), is a State corporation (Russia), state corporation of the Russian Federation responsible for space science, space flights, List of space agencies, c ...
as one of two Russian instruments onboard TGO.
[ The instrument was funded by Roscosmos and ]Centre national d'études spatiales
CNES () is the French national space agency. Headquartered in central Paris, the agency is overseen by the ministries of the Ministry of Armed Forces (France), Armed Forces, Ministry of Economics and Finance (France), Economy and Finance and Min ...
(CNES) of France, and has components of both Russia and France. Its development and fabrication was under Russian leadership. The functionality of all the three channels was confirmed during cruise to Mars.
Objectives
The main objective of the ACS suite is to make an inventory and map minor atmospheric species or trace gases in the atmosphere of Mars
The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.85%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and nob ...
. This will allow scientists to profile the upper limits on the methane contents, and to possibly to detect sulfur dioxide ( ), a gas of volcanic origin.
Channels
The near-infrared
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those of ...
channel (NIR), is a compact spectrometer operating in the range of 0.7–1.7 μm
with a resolving power of λ/Δλ ~ 20,000 and with a spectral range of 10–20 nm. It is designed to operate in nadir
The nadir is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface.
The direction opposite of the nadir is the zenith.
Et ...
and in solar occultation modes.
The mid-infrared channel (MIR) is an echelle spectrometer with crossed dispersion, designed exclusively
for solar occultation measurements in the 2.2–4.4 μm spectral range with a resolving power of approximately 50,000.
The far-infrared channel covers the thermal infrared spectroscopy
Thermal infrared spectroscopy (TIR spectroscopy) is the subset of infrared spectroscopy that deals with radiation emitted in the infrared part of the electromagnetic spectrum. The emitted infrared radiation, though similar to blackbody radiation, ...
; it is a Fourier spectrometer called the TIRVIM. It has an aperture of ~5 cm and it measures the spectrum of 1.7–17 μm. Its main task will be for temperature sounding of the Martian atmosphere
The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95%), molecular nitrogen (2.85%), and argon (2%). It also contains trace levels of water vapor, oxygen, carbon monoxide, hydrogen, and nob ...
in the 15-μm band. TIRVIM has 10 times higher
performances than the PFS spectrometer of Mars Express
''Mars Express'' is a space exploration mission by the European Space Agency, European Space Agency (ESA) exploring the planet Mars and its moons since 2003, and the first planetary mission attempted by ESA.
''Mars Express'' consisted of two ...
orbiter.
Methane
Of particular interest to this astrobiology mission, is the detection and characterization of the atmospheric methane
Atmospheric methane is the methane present in Earth's atmosphere. The concentration of atmospheric methane is increasing due to methane emissions, and is causing climate change. Methane is one of the most potent greenhouse gases. Methane's radiati ...
(), as it may be of geological or biological nature. Large differences in the abundances were measured between observations taken in 2003, 2006, and in 2014 NASA reported that the ''Curiosity'' rover detected a tenfold increase ('spike') in methane in the atmosphere in late 2013 and early 2014. This suggests that the methane was locally concentrated and is probably seasonal. Because methane on Mars would quickly break down due to ultraviolet radiation from the Sun and chemical reactions with other gases, its persistent presence in the atmosphere also implies the existence of an unknown source to continually replenish the gas.
Measuring the ratio of hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
and methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
levels on Mars may help determine the likelihood of life on Mars
The possibility of life on Mars is a subject of interest in astrobiology due to the planet's proximity and similarities to Earth. To date, no conclusive evidence of past or present life has been found on Mars. Cumulative evidence suggests that ...
. According to the scientists, "...low H2/CH4 ratios (less than approximately 40) indicate that life is likely present and active."
References
{{Satellite and spacecraft instruments
ExoMars
Astrobiology
Scientific instruments
Mars imagers
Spacecraft instruments
Geophysical imaging
Spectrometers