The United Arab Emirates' Mars Hope probe, orbiting the Red Planet since
February, has captured images of a very rare and spectacular event: a
nocturnal aurora. The probe is equipped with an ultraviolet spectrometer,
designed to study the process of escape into space of oxygen and hydrogen from
the atmosphere of Mars; the sensitivity of the instrument made it possible to
capture by chance a magnificent discreet aurora in the Martian night.
The nocturnal auroras of Mars are particularly difficult to detect and
scientists have been trying to study the phenomenon in detail for several
decades. Just five months after arriving, Mars Hope is already making a
major discovery, which was not even part of the mission's original science
goals: Images released last week show large, luminous structures in the
planet's dark skies.
“[These auroras] aren't easy to grasp, and that's why seeing them right away
with Emirates Mars Mission was quite exciting and unexpected,” said Justin
Deighan, planetologist at the University's Atmospheric and Space Physics
Laboratory. of Colorado and scientific leader of the Hope mission. This
discovery could help better understand the Martian atmosphere and how it
interacts with solar activity.
"Mini magnets" spread all over the planet
On Earth, the polar auroras are linked to the magnetic field of our planet;
they occur when charged particles from the solar wind collide with the
magnetosphere. These high-energy particles are captured and channeled by the
lines of the earth's magnetic field to the poles; there, they excite and
ionize the atoms of the upper atmosphere which, returning to a more stable
state, emit a photon. A “curtain” of various colors then appears in the sky,
due to the various gases present in our atmosphere.
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| Images taken by Hope’s onboard spectrometer (left-hand panel) and an artist’s impression (right) show discrete auroras on Mars’s night side.Credit: Emirates Mars Mission |
On Mars, the process is very different: Auroras are not limited to the
poles, but can appear all over the planet. Unlike Earth, Mars does not have
(or rather, no longer has) a global magnetic field, comparable to that of a
giant right magnet. On the surface of the red planet, however, scientists
have detected plates of rock containing the signature of a magnetic field
that has now disappeared. “It's like you've taken a bag of magnets and
thrown them into the crust of the planet. They are all pointed in different
ways and they have different strengths,” says Deighan .
Finally, these disjointed magnetic fields act a bit like lenses guiding the
particles of the solar wind towards different parts of the Martian
atmosphere; these particles then collide with atoms and molecules in the
upper atmosphere, generating the glow of the aurora. Scientists have
observed three types of aurora on Mars. One of them occurs exclusively on
the side lit by the Sun; the other two occur at night. Among these nocturnal
phenomena, one only occurs during extremely powerful solar storms. Discrete
auroras, such as the one captured by Hope, are not limited to intense solar
activity and only occur in certain areas of the night side of Mars, where
traces of ancient magnetism are particularly dense.
Elucidate the disappearance of the atmosphere of Mars
Although it was not designed specifically for this use, the EMUS (Emirates
Mars Ultraviolet Spectrometer) on board the Hope probe had every chance of
capturing the phenomenon. "The aurorae are weak and all visible light
sensitive instruments on Mars are designed to take pictures in daylight,"
explains Justin Deighan. But EMUS can make observations in the far
ultraviolet and its position offers a global view of the planet from several
angles.
The study and comparison of the terrestrial and Martian auroras is of
particular interest to scientists, since the two planets have very different
magnetic properties. On Mars, the residual magnetism of the planetary crust is
up to 30 times that of the earth's crust, especially in parts of the southern
hemisphere. These new images provided by Hope can notably help to understand
how Mars lost its atmosphere, which was much thicker billions of years ago.
“The question is how does the energy get into the system and move away from
the upper atmosphere, and the auroras are right at the heart of that,” says
Deighan.
The team still doesn't know precisely which charged particles create these
auroras. Deighan believes that the electrons are responsible, although these
can come either from the Sun or from Mars itself; it is in all cases certain
that their energy is limited.
NASA's MAVEN probe can also take pictures of Martian aurorae when its
elliptical orbit takes it far enough away from the planet; it can also
directly measure and identify the solar particles causing the spectacle when
it is nearby. But it does not have the capacity to perform both measurements
simultaneously. So by coordinating the Aurora photographs from the Hope
spacecraft with the particle measurements from MAVEN, planetologists might
be able to better understand the nocturnal lights of Mars and determine
where the charged particles are coming from. phenomenon.
The Hope mission is scheduled to last one Martian year (or 687 Earth days),
which will allow the team to collect much more information about these
particular auroras. “We are able to capture these kinds of images on a very
regular basis, so we would expect more frequent images of the aurora each time
they occur, and this will allow us to further study the discrete auroras and
why they occur. produce”, explains Hessa Al Matroushi, responsible for the
mission.
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Space & Astrophysics