Space Sunday: pebbles, ALH84001 and a supernova

Mars 2020 rover Perseverance. Credit: NASA/JPL

NASA’s Mars 2020 rover Perseverance rover is suffering what might considered a case of kidney stones that’s proving hard to clear up.

On December 29th, 2021, the rover drilled into a rock the mission team had dubbed “Issole”, coring the material out using the percussive drill at the end of its 2.1 m robotic arm. The coring went smoothly enough, the sample being cached inside one of the titanium tubes used for obtaining sample that are to be geocached on Mars for future collection by a joint NASA-ESA sample-return mission, however, it was then that a problem occurred.

The rover’s sample-gathering system is actually extremely complex, comprising three separate robotic systems. The first is the robot arm itself, which houses the drill mechanism and bit.

Mars 2020 SHArm robotic arm: hidden underneath the rover, SHArm is responsible for handling sample tubes (highlighted in yellow) before / after they have been used to gather core samples gathered by the rover’s drill. Credit: NASA/JPL

The second is another robot arm called SHArm – the Sample Handling Arm -, tucked into the underside of the rover. Its function is to select unused sample tubes from the storage cache at the back of the rover, and pass them forward so that they can be made available to the robot arm and the drill for sample gathering. This also takes tubes containing samples and delivers them to a number of sub-systems before sealing them and stowing them back into the cache area.

Between these two, and acting as a go-between, is the “bit carousel”. This is a wheel-like robot at the front of the rover. This is a go-between for both the main robot arm and SHArm, allowing empty tubes to be delivered to a position where they can be transferred to the robot arm / drill mechanism, and full tubes to be rotated down to where SHArm can collect them. In all the carousel has capacity for up to 10 full / empty sample tubes as they are moved between the robot arm and SHArm.

The “bit carousel” (highlighted in grey) with the robot arm and the drill head it carries (the large object on the left) transferring a sample core tube (yellow) to one of its transfer recesses. Credit: NASA/JPL

It was when attempting to transfer the tube with the latest sample to the carousel that the problem occurred, prompting the mission team to order Perseverance to return the tube to the drill mechanism and then rotate the robot’s hand to allow the WATSON image to photograph the carousel – revealing small pebbles of rock were caught in the mechanism.

While the carousel is designed to operate with a degree of dirt and debris in its mechanism, the decision was taken to attempt a debris removal operation and essentially “reset” the sample gathering mechanisms. This has also proven to be a complicated operation. Firstly, the carousel had to be carefully images to understand the full extent of the debris distribution. Then the ground beneath the rover needed to be imaged for an initial set of “before” photos.

A WATSON close-up of one of the sample tube recesses in the “bit carousel”, showing some of the pebble-like debris caught in the mechanism. Credit: NASA/JPL

After this, the main robot arm was order to rotate to a position where the current sample tube could be emptied, allowing it to be re-used in a future coring of “Issole”. Then, over the course of the weekend, the entire “bit carousel” was due to be put through two rotation operations designed to help shift some of the debris. Once completed, WATSON will again be used to image the mechanism – and the ground under the rover – to ascertain the status of the debris and what further actions need to be taken to clear the remaining debris.

In all, mission engineers believe it could be the end of the week before the sample system is ready to resume operations, at which point a decision will be taken on whether or not to gather a further sample from “Issole”.

 The Riddle of ALH84001 Finally Resolved?

In 1996 a fragment of a Martian meteorite that was found in the Allan Hills, Antarctica and designated ALH84001 (marking it as the first Martian meteorite found in the area 12 years earlier, in 1984), caused a storm of controversy- which appears to now being laid to rest.

A cartoon by Kevin Kallaugher that appeared in the Baltimore Sun on August 8th, 1996 highlighting the media’s response to the ALH84001 announcement by David McKay and his team

To summarise: when parts of the meteorite were examined by a group of scientists (it is not uncommon for multiple years to pass between meteorites being found , catalogued and stored and actually being examined) announcing they may have found trace evidence of past microscopic life from Mars. Unfortunately, the press responded in a manner typified by a cartoon from the time.

The pronouncement, over-amplified by the press, garnered immediate push-back by others in the scientific community which in turn resulted in the science team – which included David S. McKay, Chief Scientist for astrobiology at the Johnson Space Centre, Texas, during the Apollo programme to double down on their claims they have discovered fossilised Martian bacteria.

Since then, the debate concerning how the objects –  chain structures nanometres in length resembling living organisms – and whether or not they might be organic in origin has raged back and forth – although it did diminish somewhat following McKay passing away in 2013. Not another team of scientists believe they have definitive proof that whilst the structures were organic in nature, they are not signs of life having once been active on Mars.

Instead, the new study – the result of an extensive study of ALH84001 samples and all that has been learned about it in the intervening 25 years – points to the organic structures being the result of abiotic organic chemistry – that is, they formed as a result of chemical reactions between water and rock that did not involve any genuine organic processes.

The chemical interactions likely took place around 4 billion years ago – at a time when Mars was believed to be much warmer and wetter than it is now, and a time when life might have originated on the planet. However, in the case of ALH84001, the team carrying out this study found that the organic compounds in the meteorite are closely associated with serpentine-like minerals. Serpentine is a dark green mineral, sometimes mottled or spotted like a snake’s skin, that is associated with once-wet environments.

On Earth, this kind of association between organics and serpentine is often associated with water percolating / circulating through magnesium-rich volcanic rocks change their mineral nature, producing hydrogen. If the water is slightly acidic and contains dissolved carbon dioxide, it can additionally result in carbonate minerals also being deposited…When taken together, these two processes – referred to as serpentinization in the case of the first and carbonation in the second – can result in deposits that appear to be of an entirely organic origination.

An electron microscopy image showing chain structures resembling living organisms fossilised in meteorite fragment ALH84001. Credit: NASA

Given the rocks in which ALH84001 were formed 4 billion years ago and were exposed to a long period of repeated water interaction, and the similarity they share with similar abiotic mineral deposits found on Earth, the team believes they are more than likely of a similar, non-organic origin.

However, the study doesn’t discount the potential for life to ever have arisen on Mars – it may actually strengthen it. This is because while these abiotic processes are not the result of organic processes, they do leave deposits of chemicals and minerals that can go on to help kick-start microbial life. What’s more, the sheer age of the ALH84001 marks it as the first Martian rock fragment that is old enough to provide evidence that abiotic processes were at work at a time when Mars was warm and wet – and when other processes may have been at work that might have utilised the deposited compounds to get basic life started. And if the rocks in which ALH84001 formed – there may be other similar ancient deposits on the planet that microbial life may have been leveraged.

Astronomers Witness a Star’s Death and a Supernova’s Birth in Real-Time

For the first time, a team of astronomers have imaged in real-time as a red super giant star reached the end of its life, watching as it convulsed in its death throes before finally exploding as a supernova.

The star was about 10 times more massive than the Sun and lay within the NGC 5731 galaxy about 120 million light-years away – meaning what astronomers saw actually occurred 120 million years ago.

In the summer of 2020, astronomers using the Pan-STARRS observatory on Haleakala, Maui noticed the progenitor tar suddenly go through a dramatic rise in luminosity. This warned them something massive was about to happen, focusing attention at Pan-STARRS on the star, and also brought in the W. M. Keck Observatory on Mauna kea, Hawaii Island in to observe the star as it collapsed over 130 days, before it gave a bright flash prior to its final exceptionally violent detonation into supernova SN 2020tlf..

The data from the observations is relatively boring – the star was far, far, far too far away to be actually images by either observatory, so it amounts to lines and dots on a chart. However, it has allows the event to be computer modelled. More particularly, the event has given astronomers first-hand insight into a supernova event involving a red super giant, and raised some puzzling questions.

For a red super giant to go supernova is not uncommon. Normally, however, there is a period of shrinkage and material ejection, referred to as circumstellar material (CSM) prior to core collapse. But that process generally takes place on a much longer timescales than the 130 days experienced by SN 2020tlf, suggesting something unusual or unexpected was taking place within the star.

In addition, the mysterious bright flash prior to the final detonation was unexpected and – thus far – unexplained, although it is thought it be somehow related to the ejected CSM – although astronomers are currently at a loss to explain what this might be. The flash appears to also be liked to a mammoth ejection of gas from the star, another aspect that doesn’t fit with established understanding of red super giant supernovae.

All of this adds up to the end of the star and the birth of SN 2020tlf being far more violent that has been the accepted case for red super giants. The question now is: was this event out of the ordinary for such stars, or does it reflect a more expected behaviour for them. However, given the sudden rise in luminosity witnessed ahead of the event, astronomers involved in projects such as the Young Supernova Experiment now have a clue to what to look for when seeking future potential red super giant supernovae.