NASA’s MESSENGER spacecraft, which left Earth in 2004 to study Mercury, will crash into the planet’s surface as soon as it runs out of propellant, most likely on April 30, says the US space agency.
MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) will impact the planet at 3.91 kilometres per second (8,750 mph) on the side of our Solar System’s smallest planet facing away from Earth.
Due to its location, scientists will not be able to view the exact location of impact in real time.
Earlier this month, mission control operators at Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, finalized the fourth in a series of orbit correction manoeuvres designed to delay Messenger’s impact into Mercury’s surface.
MESSENGER’s achievements are impressive. (Image: nasa.gov/mission)
Despite being one of our nearest planetary neighbours, not much was known about the Sun’s nearest planet before the MESSENGER mission.
John Grunsfeld, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington:
“For the first time in history we now have real knowledge about the planet Mercury that shows it to be a fascinating world as part of our diverse solar system. “While spacecraft operations will end, we are celebrating MESSENGER as more than a successful mission. It’s the beginning of a longer journey to analyze the data that reveals all the scientific mysteries of Mercury.”
MESSENGER travelled for over 6.5 years before being inserted into orbit around Mercury on 18 March, 2011.
The probe’s main mission was to orbit Mercury and gather data for one Earth year.
“The spacecraft’s healthy instruments, remaining fuel, and new questions raised by early findings resulted in two approved operations extensions, allowing the mission to continue for almost four years and resulting in more scientific firsts.”
Water ice found on Mercury
One major science finding in 2012 provided convincing evidence that Mercury harbours abundant frozen water and other volatile materials (liquids that evaporate readily) in its permanently shadowed polar craters.
Artist’s rendering of the MESSENGER spacecraft. (Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
According to MESSENGER’s data, Mercury’s polar regions have enough ice to cover an area the size of Washington more than two miles thick.
Scientists for the first time started seeing clearly a chapter in the story of how the inner planets, including Earth, got their water and some of the chemical building blocks for life.
A dark layer covering most of the (water) ice deposits backs the theory that organic compounds, as well as water, came from the outer solar system to the inner planets and could have led to prebiotic chemical syntheses, and thus, life on Earth.
Sean Solomon, MESSENGER mission’s principal investigator, and director of Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York, said:
“The water now stored in ice deposits in the permanently shadowed floors of impact craters at Mercury’s poles most likely was delivered to the innermost planet by the impacts of comets and volatile-rich asteroids. Those same impacts also likely delivered the dark organic material.”
Water ice exists at Mercury’s south pole. (Image: Nature)
Many technological firsts
Apart from an impressive list of science discoveries, the MESSENGER mission also provided a number of technological firsts, including the development of a vital heat-resistant and highly reflective ceramic cloth sunshade that protected the probe’s instruments and electronics from direct solar radiation – crucial for mission success, given that Mercury is the nearest planet to the Sun.
The technology will help in the planning and design of future planetary missions within our Solar System, NASA says.
Helene Winters, mission project manager at APL, said:
“The front side of the sunshade routinely experienced temperatures in excess of 300° Celsius (570° Fahrenheit), whereas the majority of components in its shadow routinely operated near room temperature (20°C or 68°F).”
“This technology to protect the spacecraft’s instruments was a key to mission success during its prime and extended operations.”
Abundance of volatile elements surprised scientists
In an interview with Nature author Alexandra Witze, Sean Solomon said after being asked what surprised him about Mercury:
“The big surprise was the high abundances of volatile elements. All of the ideas for how Mercury got put together predicted that it would be depleted in volatiles, much like the Moon. But instead, we see sulphur ten times the average for Earth. We see sodium and potassium. We see chlorine, one of the most volatile elements that we have the ability to measure.”
“That means we really didn’t understand the particular way that Mercury became an iron-rich planet. It wasn’t a process with sustained high temperatures that drove off the volatile elements. I don’t think the final chapter has been written on what the most likely explanation is for the formation of Mercury.”