A close encounter with a mysterious moon

In 1877, American astronomer Asaph Corridor found two small moons circling the planet Mars, later named Phobos and Deimos after the Greek for “worry” and “panic.”

Nevertheless it was pleasure, fairly than worry and panic, that characterised the shut encounter with Phobos made by ESA’s Mars Categorical spacecraft within the run as much as Halloween this yr. The current flyby of the bigger Martian moon provided the proper alternative to check one of many 19-year-old spacecraft’s newest upgrades.

The MARSIS instrument on Mars Categorical was initially designed to check the inner construction of Mars. Because of this, it was designed to be used on the typical distance between the spacecraft and the planet’s surface—greater than 250 km.

Nevertheless it lately acquired a significant software program improve that enables it for use at a lot nearer distances and which may assist to make clear the mysterious origin of the moon Phobos.

“Throughout this flyby, we used MARSIS to check Phobos from as shut as 83 km,” says Andrea Cicchetti from the MARSIS workforce at INAF. “Getting nearer permits us to check its construction in additional element and establish essential options we’d by no means have been in a position to see from additional away. In future, we’re assured we may use MARSIS from nearer than 40 km. The orbit of Mars Categorical has been fine-tuned to get us as near Phobos as potential throughout a handful of flybys between 2023 and 2025, which is able to give us nice alternatives to strive.”

“We did not know if this was potential,” says Simon Wooden, Mars Categorical flight controller at ESA’s ESOC operations middle, who oversaw the add of the brand new software program to the ESA spacecraft. “The workforce examined just a few totally different variations of the software program, with the ultimate, profitable tweaks uploaded to the spacecraft simply hours earlier than the flyby.”

Mysterious origins

MARSIS, well-known for its function within the discovery of indicators of liquid water on the Purple Planet, sends low-frequency radio waves in the direction of Mars or Phobos, utilizing its 40-meter lengthy antenna.

Most of those waves are mirrored from the physique’s floor, however some journey via and are mirrored at boundaries between layers of various supplies under the floor.

By inspecting the mirrored indicators, scientists can map the construction under the floor and examine properties such because the thickness and composition of the fabric.

For Mars, this might reveal totally different layers of ice, soil, rock or water. However the inner construction of Phobos is extra of a thriller, and the improve to MARSIS may supply essential perception.

“Whether or not Mars’ two small moons are captured asteroids or made of fabric ripped from Mars throughout a collision is an open query,” says ESA Mars Categorical scientist Colin Wilson. “Their look suggests they had been asteroids, however the way in which they orbit Mars arguably suggests in any other case.”

“We’re nonetheless at an early stage in our evaluation,” says Andrea. “However we’ve got already seen potential indicators of beforehand unknown options under the moon’s floor. We’re excited to see the function that MARSIS may play in lastly fixing the thriller surrounding Phobos’ origin.”

What does this picture present?

The highest-right picture reveals the “radargram” acquired by MARSIS throughout the flyby of Phobos on 23 September 2022. A radargram reveals the “echoes” created when the radio sign emitted by MARSIS bounces off one thing and returns to the instrument. The brighter the sign, the extra highly effective the echo.

The continual brilliant line reveals the echo from the moon’s floor. The decrease reflections are both “muddle” attributable to options on the moon’s floor, or, extra curiously, indicators of potential structural options under the floor (e).

“Part A–C was recorded utilizing an older configuration of the MARSIS software program,” says Carlo Nenna, MARSIS on-board software program engineer at Enginium, who’s implementing the improve. “The brand new configuration was ready throughout the ‘technical hole’ and efficiently used for the very first time from D–F.”

The left and bottom-right photographs present the trail of the remark throughout the floor of Phobos.