Curiosity climbs and tilts at Mount Sharp; InSight offers surprises

by Chris Gebhardt

As the Perseverance — formerly known as Mars 2020 — rover continues preparations for its launch to Mars in July, its older cousin, Curiosity, and extended family member, InSight, continue to reveal new and fascinating features of the Red Planet.

For Curiosity, Mount Sharp has provided a new driving route to quickly reach a fascinating rock capping feature called Greenheugh pediment.  Meanwhile, InSight data reveals the surprising frequency of marsquakes as well as odd magnetic pulses at Homestead hollow. 

Curiosity – 5 Martian years on:

Since landing at Gale Crater on Mars in August 2012, the Curiosity rover has played a vital role in scientists’ understanding of how the Red Planet’s past informs its present. 

Surface features at Gale Crater and Mount Sharp continue to offer tantalizing exploration environments, with Curiosity discovering bizarre methane and oxygen fluctuations that scientists don’t yet understand in Mars’ local atmosphere.

Now, scientists are seeking to send Curiosity where it hasn’t gone before: having it climb its steepest incline yet to reach the top of the Greenheugh pediment.

Mission teams have long wanted to climb to the top of the pediment, but the access routes identified via orbital reconnaissance to this higher elevation are still months or years away from Curiosity’s current location.

Curiosity spent most of February 2020 investigating a drill site known as Hutton, where the teams marked their 24th drill into the Martian rock of the mission. 

February also marked the start of Curiosity’s fifth Martian year of operations — a milestone the rover and teams celebrated by using the CheMin (Chemical and Mineralogy) and SAM (Sample Analysis at Mars) instruments on Curiosity to analyze the mineralogy, chemistry, and isotopic composition of the Hutton drill samples.

But as the month-long Houghton drill campaign progressed, teams began to have a spirited discussion about exactly where to send Curiosity next. 

The original plan would have seen the rover retrace its steps — so to speak — and return to the original mapped out driving route along the shallower portions of the Mount Sharp incline

But the plethora of terrain images acquired by Curiosity during its Hutton campaign caused the team to consider a radical shift to the driving plan: having the rover ascend its steepest incline ever of 25° to 30° to reach the top of the Greenheigh pediment via newly identified access routes. 

In consultation with surface properties scientists, the Curiosity team identified a potential passable route to the top of the pediment that Curiosity could reach from its current location without having to backtrack. 

Changing the rover’s driving plan is always a possibility, though its effect on other scientific investigations have to be taken into account. 

Image taken by the Mast Camera (Mastcam) onboard Curiosity on Sol 2693. (Credit: NASA/JPL-Caltech)

In this particular case, the entire Curiosity team decided the science benefits of sending the rover to the top of the pediment now outweighed the potential risks of the steep incline drive.

Curiosity began the process of driving to the top of the pediment on 26 February.

Speaking of the decision, Abigail Fraeman, Planetary Geologist at NASA’s Jet Propulsion Laboratory, siad, “We’ve never driven up slopes this steep with Curiosity before, and we don’t actually know if the rover will be able to make it all the way up and over.  However, all of our analysis shows this attempt won’t put any unusual risk on the vehicle hardware, so there’s no reason we can’t try!”

By 2 March, the rover had completed the first in its series of drives and was at a stable 26.7° tilt at its highest-yet achieved elevation at Mount Sharp.

The ChemCam and Mastcam instruments were then used to sample and characterize the bedrock underlying the pediment capping rock before continuing to drive.

During this next drive, Curiosity reached a tilt of more than 30° — which is a record for Curiosity but not the all-time tilt record, which is held by Opportunity at 32° reached on 10 March 2016 while investigating Knudsen Ridge at Endeavour Crater.

But the Curiosity driving plan soon changed again, and driving was stopped when a batch of imagery from the rover revealed interesting features related to “possible contact between the Murray (sediment layer) and the overlying pediment,” noted a NASA blog post on 3 March.

As Susanne Schwenzer, Planetary Geologist at The Open University, related, “Changing the plan from ‘keep moving’ to ‘stay’ is never taken lightly, and the discussions reflected this as we were weighing options. 

“The reason for the discussion was that we found a site close to the contact that looked much more accessible, detail rich and valuable up close than it had originally looked from the bottom of the hill.  This justified not driving all the way onto the top of the pediment today, and instead doing a small adjustment to allow us to do contact science at these interesting targets” on 4 March.

By the following Earth day, Curiosity was near the top of the pediment, with all drives going well.

The rover was on a 26° slope getting ready for “contact science” with the geology of the region.

InSight — marsquakes and magnetic pulses:

Since its landing in November 2018 in Homestead hollow, a region on the Elysium Planitia of Mars, the stationary InSight lander has gathered unique and first-of-its-kind data on Mars’ interior, equated colloquially to giving the planet a health check-up or physical for the first time.

InSight is the first mission dedicated to looking deep beneath the Martian surface.  Among its science tools are a seismometer for detecting quakes and a magnetometer.

While the news-catching scientific instrument has been a heat probe burrowing itself deep into the Martian surface, the lander itself is also an atmospheric and surface characterization and investigation platform.

And both the interior and exterior environments of Mars have yielded fascinating results just one year into InSight’s two year planned mission.

One of the most fascinating results so far comes from the Seismic Experiment for Interior Structure, or SEIS, that detects marsquakes.

The frequency of these quakes is far greater than initially anticipated, but the magnitude of the tremors are also far milder than first hypothesized.

Since its deployment onto the Martian surface, SEIS has detected at least 450 distinct seismic events, which investigators believe are largely marsquakes with a few being “data noise created by environmental factors, like wind.”

The largest of the marsquakes detected so far was a 4.0 tremor on the moment magnitude scale.

While it took a couple months to deploy and calibrate SEIS after InSight landed, the experiment is currently recording approximately two marsquakes or seismic events every day. 

The two largest quakes detected by InSight appear to have originated in a region of Mars called Cerberus Fossae.
(Credit: NASA/JPL-Caltech/Mars Reconnaissance Orbiter/University of Arizona)

Scientists hope the experiment will eventually capture a marsquake much larger than the 4.0 moment magnitude quake already detected, for larger quakes are the ones whose seismic waves can penetrate below the crust and into the planet’s lower mantle and core. 

According to Bruce Banerdt, InSight’s Principal Investigator at JPL, “Those are the juiciest parts of the apple when it comes to studying the planet’s inner structure.”

While the underlying mechanism behind marsquakes are different than the tectonic activity responsible for the vast majority of Earth’s temblors, the resulting seismic waves still reveal a great deal about the planet’s interior as they bounce off the various structures that probes, rovers, and landers cannot see from orbit or the planet’s surface.

Pinpointing the exact origin of some of these small marsquakes can be difficult, but a pair of marsquakes have been definitively traced to the region of Cerberus Fossae, where ancient floods carved channels nearly 1,300 kilometers long into Mars’ surface. 

Lava flows then seeped into those channels within the past 10 million years; and its these lava flows that show signs of having been fractured by quakes less than 2 million years ago.

“It’s just about the youngest tectonic feature on the planet,” said planetary geologist Matt Golombek of JPL. “The fact that we’re seeing evidence of shaking in this region isn’t a surprise, but it’s very cool.”

Shifting to the surface, one of the most fascinating developments so far from the InSight mission has been the detection of magnetic signals 10 times stronger than scientists thought possible based on orbital observations and measurements of Mars’ current magnetic environment.

It’s known that Mars used to have a magnetic field that protected it and much of its atmosphere from the solar wind and magnetized the rocks of the planet.

That magnetic field disappeared as Mars’ mantle and core solidified.  As the magnetic field dissolved, so did its ability to magnetize new rocks forming on Mars.

But new research from InSight shows local magnetic signals and magnetization at Homestead hollow 10 times stronger than predicted, opening the question of how the local rocks could be magnetized to such a degree when they are too young to have been magnetized by the planet’s former magnetic field.

“This magnetism must be coming from ancient rocks underground,” said Catherine Johnson, a planetary scientist at the University of British Columbia and the Planetary Science Institute. 

“We’re combining these data with what we know from seismology and geology to understand the magnetized layers below InSight.  How strong or deep would they have to be for us to detect this field?”

Yet another fascinating and complicating part of this magnetic puzzle at Homestead hollow is that the magnetic signals change over time, varying in intensity between day and night with observations showing that the magnetic properties of the region “pulse” around midnight every day.

This strange variations and pulsing could have something to do with how Mars’ atmosphere reacts to the solar wind, but much more data will be needed before a firm hypothesis can be formed.

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