The MER rovers first arrived on Mars at the start of 2004. One, Opportunity, is still operating today (credit: NASA / JPL)
Spirit, one of NASA’s two solar-powered Mars Exploration Rover (MER) missions, may have ceased communications with Earth on March 22nd, 2010 and the mission declared over on May 24th, 2011, but its science legacy lives on.
Originally designed with a 90-day primary mission duration, Spirit massively exceeded this, ranging across Mars for a distance of 7.73 kilometres (4.8 mi) over 1,944 days of mobile operations before becoming bogged down in a sand trap on May 1st, 2009, almost 5.5 years after it had arrived on Mars, after which it operated as a stationary research programme for a further 751 days.
During its mobile period, Spirit explored a small rocky plateau dubbed “Home Plate” in 2007 / 2008. Whilst exploring the rock, the rover imaged several peculiar small rock formations resembling cauliflower or coral. Analysis by the rover’s Mini-Thermal Emission Spectrometer (Mini-TES) revealed the formations to be almost pure silica (SiO2), a mineral associated with volcanic environments.
Silica is formed when water (rain or snow) seeps underground and comes into contact with rocks heated from below by magma. Itself super-heated by the rocks, the water is vaporised and rises back through the ground, dissolving silica and other minerals as it does so, which it deposits around the vents or fumaroles it uses to escape back into the atmosphere.
the “cauliflower” or “coral” formations imaged by MER rover Spirit around the “home Plate” plateau in 2008 (credit: NASA / JPL)
Warm, rich in silica and minerals, on Earth these fumaroles and vents become havens for bacterial life which is known for creating curious bulbous and branching shapes in silica formations here on Earth which are strikingly similar to those imaged by Spirit. Such is the similarity, that planetary geologist Steven Ruff and geology professor Jack Farmer, both from Arizona State University, have been carrying out detailed studies in the high Atacama Desert, regarded as the most arid non-polar region on Earth, harbouring conditions thought to be very similar to those of ancient Mars.
In particular, they have been investigating the remote geyser fields of El Tatio, some 4.3 km above mean sea level in an environment which has much in common with the Gusev Crater region of Mars, where “Home Plate” resides. This includes being exposed to high levels of ultraviolet light from the sun and extreme temperatures. Their investigations revealed forms they call “micro-digitate silica structures” which are both remarkably similar to the formations on Mars, and to those found around fumaroles and vents at lower altitudes here on Earth which are formed by bacteria.
A comparison between images of the formations found on Mars by the MER Spirit (top right), and those imaged by Ruff and Foster in El Tatio, Atacama Desert (credit: S. Ruff, Arizona State University)
While the pair have yet to come up with definitive evidence that the El Tatio formations are the result of microbial activity, they believe the objects may be “micro-stromatolites”. Nornally of a much larger size, stromatolites are formed by bacteria “cementing” mineral grains together to form a thin layer. Over time, these layers accumulate one over the last, forming a laminar mound or rock. The oldest stromatolites on Earth are estimated to be some 3.5 billion years old, a time when both Earth an Mars may have shared much closer atmospheric and geological similarities. So, if the formations found at El Tatio do prove to be the result of bacterial activity, then it offers a hypothesis that the formations on Mars may also have been the result of bacterial activity.
Dream Chaser: the Dream is Alive
In January, I wrote about NASA’s surprise decision to award an extended contract for uncrewed resupply missions to the International Space Station to both of the existing contract holders, SpaceX and Orbital ATK, and to Sierra Nevada Corporation, who will use an uncrewed variant of their Dream Chaser space plane. At the time I wrote that update, reader Devin Vaughn indicated an interest in learning more about Dream Chaser, which has an interesting heritage.
As I noted at the time, the vehicle had been one of four private sector contenders to fulfil the role of “space taxi”, ferrying up to 6 at a time from US soil to the ISS. The idea being that by spinning-out the ISS crewed flights to the private sector (with financial support from NASA), the US agency could focus its manned space flight development programme solely on the Orion / SLS programme, which is intended to form the nucleus of US (and possibly international) crewed mission ventures well beyond Earth orbit.
Dream Chaser was unique among the commercial crew transportation proposals as it was based on a “lifting body” design , allowing to re-enter the Earth’s atmosphere and glide to a landing on a conventional runway – aspects which still make it a very flexible vehicle (credit: SNC)
Dream Chaser ultimately wasn’t selected for the crewed mission contract – which caused some friction between Sierra Nevada Corporation and NASA when it was announced in 2014 – but the US space agency continued to work with SNC to help develop the vehicle, with the Dream Chaser Cargo variant being the result – although SNC has not given up on developed the crewed version of the vehicle.
Dream Chaser Cargo is designed to fly up to 5 tonnes of cargo to / from orbit. This can be both pressurised and unpressurised material, and the vehicle includes the ability for unpressurised cargo to be directly transferred from its cargo module to the exterior of the space station should this be required. As with the original crewed variant, Dream Chaser Cargo will launch atop a rocket, but return to earth to make a conventional runway landing, the latter greatly speeding up the transfer of returned cargo (e.g. science experiments material, etc.) from the vehicle to its intended destination.