Space Sunday: moving a mole and Planet Nine

InSight’s scoop gently presses against the top of the “mole” of the HP³ experiment, ready to gently push it down into the Martian regolith. Image Credit: NASA/JPL

NASA and its partner, the German Aerospace Centre (DLR) finally have some good news about the Heat Flow and Physical Properties Package, or HP³, carried to Mars by the InSight Lander: they’ve made some progress towards perhaps getting moving again.

As I’ve noted in past Space Sunday articles, the experiment has been a source of consternation for scientists and engineers since InSight arrived on Mars in November 2018. Following the landing, HP³ was one of two experiment packages deployed directly onto the surface of Mars by the lander’s robot arm. One of the key elements of the experiment is the “mole”, a self-propelled device designed to drive its way some 5m into the Martian crust, pulling a tether of sensors behind it to measure the heat coming from the interior of Mars.

After a good start, the probe came to a halt with around 50% of its length embedded in the soil. At first it was thought it had hit solid bedrock preventing further motion; then it was thought that the mole was gaining insufficient traction from the hole walls, on account of the fine grain nature of the material it was trying to move through. That was in February 2019.

The InSight lander was commanded to deploy the HP3 drill system on February 12th, 2019. Credit: NASA/JPL

Since then, scientists and engineers have been trying to figure out what happened, and how to get the mole moving again – because of the delicate nature of the sensor tether, the HP³ experiment couldn’t simply be picked up and moved to another location and the process started over. instead, various attempts were made to try to giving the mole material so it might gain traction.

Most of these revolved around using the scoop at the end of the lander’s robot arm to part-fill / part compress the hole created by the mole, the theory being that loose regolith would gather around the head of the mole and help it regain the necessary fiction to drive itself forward once more. Initially, some small success was had – until the mole abruptly “bounced” almost completely back out of the hole.

Further attempts were made to compress the ground around the hole, but all forward motion remained stalled, leading scientists to believe the mole had struck a layer of “duricrust” – a hard layer formed as a near the surface of soil as result of an accumulation of soluable materials deposited by mineral-bearing waters that later leech / evaporate away. These layers can vary between just a few millimetres to several metres in thickness, and are particularly common to sedimentary rock, which itself has been shown to be common on Mars.

The rub for the InSight mission is that if it is a layer of duricrust beneath the lander, it is impossible to tell just how thick it might be.

This images shows how difficult “pushing” the mole would be. The scoop (upper right) had a very small surface area at the end of the mole with which it could safely make contact, shown circled, without potentially damaging the tether harness. Credit; DLR

Earlier this year it was decided to use the scoop on the robot arm more directly, positioning it over the exposed end of the mole and applying pressure in the hope it could push the mole gently down into the ground in a series of moves that would allow the mole to get to a point were it could resume driving itself into the ground.

However, this approach has not been not without risk. The end of the mole has a “harness” – a connector for the tether, so the scoop has to be precisely positioned and any sort of pressure applied very gently and carefully to avoid any risk of slippage that might result in damage to the tether and / or harness and render its ability to gather data and information from the probe useless.

However, on June 3rd, NASA announced that a series of gentle pushes had resulted in the mole being completely below the surface, and with no apparent damage to the tether or harness. However, whether or not this means the mole is able to proceed under is own self-proplusion is unclear, as NASA noted in their tweet.

In all, the tip of the mole is now some 3m below the Martian surface. That’s deep enough for it to start registering heat flow, but to be effective, the mole still needs to drive itself down the full 5 metres. It is only at this depth that the mole and sensors can correctly start to measure the sub-surface geothermal gradient, and thermal conductivity, the two pieces of information required by scientists to obtain the heat flow from deeper in the planet. By studying the thermal processes in the interior of the planet, scientists can learn a lot about the history of Mars, and how it formed. They may also gain insights into how other rocky bodies formed.

Attempts have yet to be made to see if the mole can move under its own spring-driven propulsion, but for now NASA and DLR are rightly treating the current status of the probe as a victory. The tether harness at the end of the mole is undamaged, so if the mole can resume progress under its own power, there’s not reason why it shouldn’t start recording information.

Bye-Bye Planet Nine

I’ve covered the conundrum of Planet Nine  – or “Planet X”, “George”, “Jehoshaphat”, or “Planet of the Apes”, depending your preference – numerous times in Space Sunday (see here, here, and here for more).

As a brief recap: a group of astronomers noted that a number of Kuiper Belt Objects (KBOs) occupied highly unusual orbits around the Sun compared to their brethren. These objects include Sedna, the minor planet discovered in 2003 and which orbits the Sun once every 11,000 years in an orbit that varies between 76 AU at perihelion to 936 AU at aphelion.In particular, the astronomers noted that all of the objects were in orbits well beyond any distance at which they might be influenced by Neptune or the other planets. So the theory came about that there must be a large planet lurking far out in space, perhaps 200 AU from the Sun, and itself in a highly inclined orbit that had teased the objects into their unusual orbits.

It had been thought that Planet Nine, if it exists, might equal Neptune in size, and orbits the Sun 200 times further away than Earth. However, another study casts further doubt on its existence. Credit: Caltech / R. Hurt

And so in 2016 the hunt for Planet Nine started. But despite computer modelling using the orbits of Sedna and its fellows to try to predict the likely orbit “Planet Nine would be in, and calculations on where in that orbit it might conceivably be, it has remained elusive – to the extent that the doubts that always existed about its presence started to multiply.

In January 2020 I wrote about a study from the Colorado University that offered natural explanations for the odd orbits of the KBOs associated with the idea of Planet Nine. Now a further group, led by Professor Samantha Lawler, an assistant Professor of Astronomy at the University of Regina, Canada. she and her team have been carrying out a continuous 5-year study into KBOs using the Canada-France Hawaii Telescope, and the processes that shape their orbits, including the influence of large actual or theoretical planetary bodies. Based on her team’s findings, she believes it is time to put the entire idea of Planet Nine to bed.

Through their work, Lawler and her team have found a large number of KBOs in extended and highly elliptical / eccentric orbits. These orbits simply cannot, collectively, be explained by the idea of a planet laying far, far out from the Sun pushing them into those orbits. Instead, she believes there is a much more direct explanation. When r – many of them which simply do not confirm with the idea of a far out planet orbiting the Sun and pushing them into those orbits.

Computer modelling to try to define Planet Nine had been based on the eccentric orbits of a handful of seasonally-visible KBOs. Credit: Caltech / R Hurt

The Planet Nine theory does not hold up to detailed observations. The discoveries from the most successful Kuiper Belt survey to date, the Outer Solar System Origins Survey (OSSOS), suggest a sneakier explanation for the orbits we see, and it all has to do with Neptune.

– Professor Samantha Lawler

Simply put, the Nice Model of the solar system’s evolution, first proposed in 2005,states that the giant planets of the solar system were originally in a much more compact configuration, but over time they migrated outwards, gradually achieving a stable resonance in their respective orbits.

Whilst a relatively new theory, the Nice Model helps explain historical events including the Late Heavy Bombardment of the inner Solar System, the formation of the Oort cloud, and the existence of populations of small Solar System bodies including the Kuiper belt, the Neptune and Jupiter trojans, and the numerous resonant trans-Neptunian objects dominated by Neptune.  In particular, Lawler and her team have been able to show through computer modelling that almost all of the eccentric orbits of KBOs  – including those of Sedna and Co. – can be accounted for by Neptune’s migration outwards from the Sun as proposed by the Nice Model.

When the OSSOS study data for extreme KBOs is compared to the DES study (used as a basis for the Planet Nine Modelling) and other studies, it reveals a far greater range of KBOs in eccentric orbits, many of which can be explained by the Nice Model’s hypothesis that Neptune has migrated outward from the Sun during the early history of the solar system. Credit: Samantha Lawler

Lawler admits not all of the eccentric KBO orbits can be explained by Neptune’s migration, but more than enough fit the simulations her team has developed, that it does seem that Neptune is far more likely to be responsible for pushing Sedna and the other KBO into their current orbits than Planet Nine.

Virgin Orbit: Test Flight Failure, UK Hopes

Amidst all the SpaceX / NASA excitement with the launch of the Demo-2 Crewed Dragon mission and the loss of Starship prototype SN4 (see my previous Space Sunday report), I didn’t have time to update on Virgin Orbit.

On May 25th, the company attempted to make their first orbital test flight of their LauncherOne rocket. Intended as a low-cost means of launching small satellites of up to 500 Kg, LauncherOne is designed to be lifted to altitude by a carrier aircraft before being released and allowed to fire its motor to accelerate to orbit.

May 25th: a chase plane captures the moment LauncherOne ignites its motor as Cosmic Girl climbs away from the rocket. Unfortunately, the rocket engine failed seconds later, ending the planned orbital test flight. Credit: Virgin Orbit

For the test launch, which was not live streamed, the rocket was carrying a dummy payload. Initially, things went well enough. The company’s Cosmic Girl launcher aircraft, a modified Boeing 747, took off from the Mojave Air and Space Port in California at 11:56 PST, and performed a 54-minute flight to the launch zone off the Southern California coast whilst climbing to an altitude of 10,000 metres prior to releasing the rocket.

Initially, LauncherOne’s motor ignited as planned, but a few seconds later, an “anomaly” occurred, and the motor shut down. The vehicle was “terminated” shortly after the shut down, ending the attempt. Virgin Orbit are still reviewing the flight data to determine what happened, and whether changes need to be made to the rocket or its motor ahead of any further attempt to make a launch.

In the meantime, the company and the UK government have announced they are to push head with plans for Virgin Orbit to offer satellite launches out of Cornwall Airport Newquay, in the south-west of the country, and possibly elsewhere. Specifically, Virgin Orbit has been granted permission to issue request for proposals from UK companies for a transportable ground operations system (TGOS), a collection of tanks, generators and other systems used to fuel and prepare the LauncherOne rocket for flight.

Virgin Orbit hopes to commence operations out of the UK’s Spaceport Cornwall in 2021/22 Credit: CAN

The TGOS system will used for LauncherOne operations out of Cornwall Airport Newquay, also known as Spaceport Cornwall, and as it is intended to be air-transportable, it will allow Virgin Orbit to potentially offer launches services elsewhere, subject to agreements being reached with suitable airports.

If all goes according to plan, Virgin Orbit plan to have the TGOS operational at Spaceport Cornwall by mid-to-late 2021, allowing them to commence launches there either before the end of 2021 or in early 2022.