Space Sunday: exoplanets and Mars missions

An artist’s impression of Proxima-b with Proxima Centauri low on the horizon. The double star above and to the right of it is Alpha Centauri A and B. Credit: ESO

In 2016, astronomers reported their discovery of a planet orbiting our nearest stellar neighbour, Proxima Centauri (see: Space Sunday: exoplanets, dark matter, rovers and recoveries). Since then, the debate has swung back and forth on the potential of it being suitable for life.

While the planet – called Proxima-b – lies within it’s parent star’s habitable zone, there are, as I’ve previously reported, some significant barriers to it being a potential cradle for life. In particular, red dwarf stars are volatile little beasts (Proxima Centauri is just 1.5 times bigger than Jupiter), with their internal activity convective in nature. This tends to give rise to massive stellar flares that can bathe planets orbiting them in high levels of biologically harmful radiation. In addition, many planets discovered orbiting red dwarfs are so close to their parent as to be tidally locked – always keeping the same face towards their sun. This means they are liable to extremely hostile conditions: high temperatures on one side, freezing cold on the other, with the region around the terminator liable to violent weather – assuming they have an atmosphere; over longer periods of time, the onslaught of X-ray radiation and charged particle fluxes from their parent star can literally strip away any atmosphere, unless a planet can replenish it fast enough.

This latter point is the conclusion reached by a team of scientists at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland in reference to Proxima Centauri b in 2017 (see: Space Sunday: Curiosity’s 5th, Proxima b and WASP-121b), although they were working largely from computer modelling.

The Earth-sized Proxima-B and its parent star

However, all that said, if Proxima-b does still have an atmosphere, then a new study conducted by researchers from the Carl Sagan Institute (CSI) suggests life might have got started on Proxima-b, and might even still exist there.

In essence, the team from CSI examined the levels of surface UV flux that planets orbiting M-type (red dwarf) stars like Proxima-b would experience and compared that to conditions on primordial Earth. At that time, some 4 billion years ago, Earth’s surface was hostile to life as we know it today, thanks to a volcanically toxic atmosphere and the levels of UV radiation reaching the surface from the Sun; however it is believed the it was the period when life first arose on Earth.

In particular, the team modelled a range of possible surface UV environments and atmospheric compositions of four nearby “potentially habitable” exoplanets: Proxima-b, TRAPPIST-1e, Ross-128b and LHS-1140b. These models showed that as atmospheres become thinner and ozone levels decrease, more high-energy UV radiation is able to reach the ground – which was to be expected. But when they compared the models to those developed for Earth as it was 4 billion years ago, things got interesting: the exoplanet models suggest that the UV levels they experience are all lower than the Earth experienced in its youth, when the first (pre-oxygen) life is believed to have existed – suggesting that despite their harsh conditions, life might have gained a toehold on them.

With Proxima-b this is particularly interesting, as it is liable to be somewhat older than the Earth, possibly by as much as 200 million years. This means there is a possibility that if simple life arose there early enough after the planet’s formation, it might well have had enough time to adapt to the development environment as atmospheric conditions changed, and thus survived through to current times.

The news from Proxima Centauri doesn’t end there. A team of researchers from the University of Crete and the Observatory of Turin has found possible evidence of a second planet orbiting the star.

Proxima Centauri b was identified using two instruments operated by the European Southern Observatory in Chile, which recorded “wobbles” in Proxima Centauri’s spin as a result of planetary gravitational influences. One of those instruments, called HARPS, has been the focal point for the team claiming there’s evidence for a second planet orbiting the star. By studying data gathered over the last 17 years, they believe they have found sufficient evidence to suggest a second planet could be affecting the star’s spin.

The team estimate that this second planet could have a mass approximately six times that of Earth, putting it in the category of a super-Earth / mini Neptune class of planet in terms of potential size, and that it likely orbits its parent at a distance of approximately 1.5 AU (1.5 times the average distance between the Earth and the Sun) once every 5 terrestrial years. . At such a distance, it’s likely that the surface temperatures of the planet is likely to be around -230oC.

Confirmation that the new planet does actually exists is now required – hence the research time offering their report for further peer review.

Curiosity Samples Clay on Mars

Curiosity has been on the road for nearly seven years. Finally drilling at the clay-bearing unit is a major milestone in our journey up Mount Sharp.

– Curiosity Project Manager Jim Erickson

With these words, issued in a press release on April 11th, the Mars Science Laboratory team announced a major goal for Curiosity rover had been achieved.

While it may seem are to believe, despite seven years on the surface of Mars, and with multiple drilling samples obtained, gaining a direct sample of clay rock has proven elusive. While the rover has previously sampled clay deposits and the minerals they contain, these have been contained in samples of mudstone the rover has sampled, rather than from an actual layer of clay.

“Aberlady” and the sample drill hole, April 6th, 2019. Credit: NASA/Caltech/MSSS

The primary goal for the mission is to determine whether Mars ever have the right conditions for microbes to live. It’s a question that can be answered by sampling the planet’s soil, air, and rock and carefully analysing it. This goal was actually met in the first several months of the rover’s time on Mars while it was still exploring the crater floor, but the more evidence Curiosity can gather, the clearer our understanding of past conditions in Gale Crater and on Mars become.

In this, clays play an important role. They form in water, a key requirement for life, and can act as repositories for chemical and minerals that might be indicative of conditions suitable for past life. This particular sample of clay came from a rock formation on the side of “Mount Sharp” dubbed Aberlady, which Curiosity drilled on April 6th, 2019.

As I’ve previously covered in these reports, Curiosity’s drill has had its share of issues over the years; for a time, drilling operations were completely suspended out of fears the damage one particular issue might cause if unresolved. However, clay is a relatively “soft” rock, and Aberlady was an easy target to dill and gain a sample. A few days after it hadbeen obtained, some of the sample was transferred from the drill mechanism to the rover’s on-board science laboratory, and specifically to the Chemistry and Mineralogy spectrometer, or CheMin, which will carry out an initial analysis of the material.

Gale Crater imaged by the Mars Reconnaissance Orbiter. Credit: NASA/Caltech/MSSS

In particular, the clays obtained from the sample could help could help the science team understand how wetter conditions on Mars may have helped with the formation of this part “Mount Sharp”, which comprises sedimentary rock layers, and potentially reveal more about the presence of water with Gale Crater in general.

Mars 2020 Takes Shape

In 2021, Curiosity will be joined on Mars by its sister, the Mars 2020 rover (which will doubtless receive a name between now and when it launches mid-year in 2020).

Utilising the same overall design and many similar components as Curiosity, but carrying a very different science package, the Mars 2020 mission elements are being assembled at NASA’s Jet Propulsion Laboratory (JPL) in California, and most recently several of them went through a process known as “stacking” – assembling them together to ensure they fit correctly.

This process saw the “surrogate rover”, a unit completely identical to the Mars 2020, but lacking its science equipment mounted in its “stowed” configuration on the aeroshell that will protect it during the searing entry into the Martian atmosphere. The rocket-powered “skyhook” that will deliver the rover to the surface of Mars was attached to the rover, prior to the additional of the conical aeroshell that will both help protect the rover and skyhook from the heat of entry into the Martian atmosphere and keep them shielded during the parachute descent phase of the landing. Finally, the parachute nose cone was added to the top of the aeroshell, and the completed assembly was mated to the cruise stage – the part of the vehicle which will power and protect the Mars 2020 spacecraft on its seven-month voyage to Mars.

The Mars 2020 stack (in the centre of the image) being put together in the Spacecraft Assembly Rotation Fixture (SCARF) located in the High Bay 1 clean room at JPL’s Spacecraft Assembly Facility. Credit: NASA/JPL

One of our main jobs is to make sure the rover and all the hardware that is required to get the rover from here on Earth to the surface of Mars fits inside the payload fairing of an Atlas V rocket, which gives us about 15 feet [5 meters] of width to work with. Stacking is an important milestone in mission development, because as good as our computer models are, we still need to put it together to show that the bolt holes line up and everything fits together.

– David Gruel, Assembly, Test and Launch Operations (ATLO) Manager, Mars 2020

Once assembled and checked, the entire stack was transported to the Environmental Test Facility at JPL to undergo acoustic testing. This saw the stack bombarded with a thundering wall of sound designed to imitate the sound waves generated during launch, the intention being to see fit anything can apart, fell off, or otherwise cam unstuck in a manner that might jeopardise the mission. Following an examination of the stack after this test, it is due to be transferred to JPL’s  thermal vacuum chamber, a place that simulates the harsh environment of space. Here the stack will undergo a week-long test to assess how the assembly, its system and circuitry operate under flight conditions.

And the reason a duplicate rover is being used? Simply because the actually Mars 2020 rover is still being assembled. It will also be subjected to its own testing and a further round of testing when integrated into the rest of the mission hardware, prior to being cleared for shipment from JPL to Cape Canaveral Air Force Station in readiness for its launch.

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