Welcome back!

I hope you are all safe and doing well.

To all my readers in India: Happy Independence Day!

Now that the rover Perseverance is 2 weeks closer to Mars, it is time to discuss some more of the Perseverance’s predecessors. Last time, we discussed the rover-lander combination Sojourner and Pathfinder. This time, we will discuss the next two rovers that NASA sent towards the Red Planet: Spirit and Opportunity.

Spirit and Opportunity marked a huge step-up from the Sojourner mission. They were independent moving laboratories, with considerably more ability than Sojourner, as well as with far more instruments to conduct far more detailed research into the surface of our neighbor.

But I’m getting ahead of myself. Let us take a step back and discuss this mission from the beginning: from the very idea that manifested tangibly into two of the most recognizable rovers on the Martian surface.

So sit back, relax, and enjoy the ride!

Before we go into a discussion about the rovers themselves, we must first discuss the Mars Exploration Rover (MER) mission that enabled their voyage. This mission, much like Pathfinder, had several objectives. 

The first—and mostly financial—objective of this mission was to build upon the legacy that Pathfinder had built. For a relatively inexpensive cost, two stand-alone mobile science platforms were to be placed on the surface of Mars; the total cost of the mission was about $820 million, or roughly $410 million per rover. This is comparable to the $350 million spent on Sojourner.

The second—and scientific—objective of this mission was to find traces of water in the rocks and soil found on the surface of Mars, building upon the research done initially by the two Viking landers.

Similar to Sojourner, Spirit and Opportunity were both protected from re-entry by landers, which were slowed by a combination of parachutes, retro-rockets, and airbags. Landing on different spots on the Martian equator, the lander would bloom like a lotus, and rovers would roll out and begin their research.

Here is a representation of Spirit:

In Depth | Spirit – NASA Solar System ExplorationCredit: NASA

And here is a representation of Opportunity:

 Opportunity (rover) - WikipediaCredit: NASA

Both of these rovers were identical and considerably larger than their predecessor; they were about the size of golf carts compared to the Labrador size of the Sojourner

For power, both rovers had a collection of solar panels. They had a six-wheel drivetrain with powerful suspension and wheels that could generate considerable amounts of traction. They could reach a far faste 0.11 mph, outstripping the 0.015 mph that Sojourner offered.

Both rovers also had far more scientific instruments than Sojourner. They did not have to rely on their landers to communicate with the Earth, boasting powerful radio broadcast systems of their own. They were equipped with the following:

  1. Various antennae for communication, including an X-band low-gain/high-gain antenna for Earth communication and an ultra-high frequency monopole for relaying messages
  2. Several cameras, including a color Panoramic Camera (PANCAM) for landscape images to assist with mineralogy and a monochromatic Navigation Camera (NAVCAM) with a larger field of view for navigational purposes
  3. The Miniature Thermal Emission Spectrometer (Mini-TES) to identify rocks and minerals for further examination
  4. MIMOS II, a spectrometer specializing in identifying iron and its traces in rocks
  5. An Alpha-particle X-ray spectrometer, for analysis of the abundance of elements in rocks
  6. Several magnets to collect metallic dust particles for analysis
  7. A microscopic imager (MI) for close-up analysis of rock surfaces
  8. A rock abrasion tool (RAT) for removing any weathering from rock that could potentially cover important elements to be found

As you can see, the amount and comprehensiveness of the instruments was far greater than that on the Sojourner mission! As a result, the rovers could provide far more scientific information on a much greater degree than was previously possible.

Now, let us discuss the timeline of these missions. As both rovers were to be launched separately, their launches had to be coordinated within a month of each other in order to achieve the shortest possible distance to Mars (and, therefore, the shortest time required for the flight).

The rover Spirit launched on the 10th of June, 2003, and the rover Opportunity launched on the 25th of July, 2003. They both landed in January 2004 in widely separated locations on the Martian surface.

NASA had initially intended for the mission to last 90 sols (a sol is one day on Mars, equivalent to about 40 minutes longer than a day on Earth). Once again, in true NASA fashion, the mission far outlasted the timeframe established. Spirit ended up spending a staggering 2208 sols on the Martian surface (about 6 years), traveling over 7 km (4.8 miles). Opportunity did even better than its twin, spending an incredible 5,352 sols on the Martian surface (about 15 years), traveling a jaw-dropping 45 km (28 miles); to this date, this is the farthest any off-planet vehicle has traveled. Both rovers sent a combined 10 billion bits of data back to Earth.

The last contact with Spirit was in March 2010. The rover had gotten stuck in some soft sand, in May 2009, and was struggling to escape it. NASA chose to keep the rover in place, doing studies while stationary for another year. After contact was lost, NASA attempted to regain it until May 25, 2011, when its mission was considered completed.

The last contact with Opportunity was much more recent, in June of 2018, after it went into hibernation during a large storm. It failed to reboot normally after the storm, and one year later, all attempts at re-establishing contact were given up. 

Both rovers had an undeniably large impact on the scientific advance of our knowledge of Mars. The most significant finding of the rovers was conclusive evidence of liquid water traces on the surface of Mars. Here is a brief list of more findings and the findings’ relevance.

  1. The discovery of several relevant minerals that are signs of water, including hematite, Jarosite, sulfur (as well as an ancient hydrothermal system), silicon
  2. Frost-altered rocks and surfaces, proving that the equatorial surface of Mars once had ice
  3. Evidence of lakes of acid, providing evidence of oxidation, supported by the presence of sulfate-rich rocks

Here are some images transmitted back to Earth by the rovers. All image credits to NASA|JPL.

an image of so-called grey hematite bluberries on Mars
Evidence of hematite, one of the key indicators of water

a white wheel mark in the Martian soil shows a spot where Spirit came across the mineral silica
A picture of silica (a substance found in hot springs) dragged up by Spirit’s wheels. 

a self-portrait of the Curiosity rover on MarsA panorama of the Opportunity landing site. The reflective material in the top-left of the image is the heat shield that popped off.

From the foundation forged by Sojourner, these rovers built on and developed these findings even farther, cementing their position in history as some of the most instrumental off-planet vehicles. They have rightly been considered among NASA’s most successful missions. And they helped form the foundation for Curiosity and Perseverance, the two rovers that we will discuss next time.

Remember these rovers, and have spirit, take your opportunities to heart.

Clear skies!