A spacecraft bound for Mercury may be able to take crucial measurements that could help us confirm potential signs of life seen on Venus.
On 14 September, researchers announced they had found a gas called phosphine in Venus’s clouds, and no non-biological processes that we know about could make it in such large amounts. The BepiColombo spacecraft may be able to confirm that the phosphine is indeed there.
BepiColombo is a joint mission by the European Space Agency and the Japan Aerospace Exploration Agency that launched in 2018. Before it arrives at Mercury in 2025, it will twice pass within about 10,000 kilometres of Venus, using the planet’s gravitational pull to adjust its trajectory.
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The first pass is planned for 15 October, and the BepiColombo team was already planning to make some observations of Venus to ensure the spacecraft’s scientific instruments worked. Now, with the announcement of the phosphine discovery, the team is figuring out how to use those observations to double-check the finding.
This cross-check is important because the phosphine discovery wasn’t entirely certain. When light passes through a gas like the Venusian atmosphere, certain wavelengths are absorbed, leaving dark lines in the light’s spectrum called absorption lines. Phosphine is known to absorb light at thousands of specific wavelengths, but the two telescopes that made the new discovery were only able to catch it absorbing one wavelength in Venus’s atmosphere.
“The discovery was only one line – that would be like getting a partial fingerprint, and we want lots of fingerprints,” says Sara Seager at the Massachusetts Institute of Technology, who is part of the team who discovered the phosphine. The team is now working on plans to examine the light further with Earth-based telescopes and potentially even new missions to Venus.
Luckily, BepiColombo may be equipped to get another phosphine fingerprint even sooner than those planned observations. Preliminary calculations have shown that two of phosphine’s absorption lines are in the wavelength range of one of the instruments – MERTIS, or the Mercury Radiometer and Thermal Infrared Spectrometer – that was already planned to take images of Venus as the spacecraft hurtles by, says BepiColombo team member Jörn Helbert at the German Aerospace Center.
MERTIS has two cameras that could be put to use, but getting a good shot of Venus is somewhat complicated by their configuration. The main camera is pointed towards Mercury. There is also a calibration camera that is designed to take shots of space to capture ambient light and remove its effects on the main camera’s data. As BepiColombo passes Venus, the main camera will be blocked by the spacecraft, says David Rothery at the Open University in the UK, another BepiColombo researcher, but the calibration camera might work.
Without the full resolution of the main MERTIS camera and without enough time to make any changes to the fly-by plans, it isn’t certain whether the spacecraft will be able to catch phosphine.
Luckily, there is another chance. “We have a second fly-by coming up in August 2021 where we are even closer to Venus, so if we see nothing or only something very tentative, we can try again on the second fly-by and optimise the instruments to increase our chances of detecting something,” says Helbert.
If BepiColombo does confirm that there is phosphine in Venus’s atmosphere, we are then left with the task of figuring out where exactly the gas came from – and whether it really is a sign of life.
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