April 23, 2015
MESSENGER probe is set to crash into Mercury’s surface on April 30. After being in planet’s orbit since 2011 and carrying out its mission successfully, the probe has no more fuel left and will retire in a spectacular way.
NASA’s MESSENGER probe was launched in August 2004 and it entered Mercury’s orbit in March 2011. It is the first and only aircraft to orbit the closest planet to the Sun. After one more maneuver tomorrow, it will be on a collision course with the surface on the far side of Mercury, viewed from Earth.
"We will be impacting the surface on the 30th of April, around 19:25 UTC," said Dan O'Shaughnessy, of The Johns Hopkins University's Applied Physics Lab in Baltimore, USA, systems engineer for MESSENGER mission. "That impact will not be in view. It will happen during a planetary occultation, so the spacecraft will pass behind the planet, out of view of the Earth, and will just not emerge again."
MESSENGER, which stands for MErcury Surface, Space ENvironment, GEochemistry and Ranging, is a 3 metres wide space probe, but as it slams into the surface at over 14,000 km/h, it will create a crater 15 metres across. The mission had a budget of $450 million, but the results it has achieved are far more valuable.
The MESSENGER confirmed that there is water ice and organic compounds inside Mercury's craters that are in permanent shadow, near planet's poles. It also helped create the best maps of planet's surface we have. Water and organics were probably delivered by asteroids and comets from the outer regions of the Solar System. This implies that the same scenario happened on other rocky planets, including Earth.
"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," said John Grunsfeld, associate administrator for NASA's Science Mission Directorate. "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."
Even in the afterlife, MESSENGER will be of scientific value. Since Mercury doesn’t have atmosphere, everything on its surface is exposed to space weather and bright materials turn dark with time. Knowing the exact time of probe’s impact will help future missions determine rates at which this happens.
One of those missions is European-Japanese BepiColombo probe, set for launch in 2017. When it reaches Mercury’s orbit in 2024, it will be able to observe MESSENGER’s resting place, something we will not be able to do from Earth.
"Having an impact crater, even a small one, whose origin date is precisely known, will be an important benchmark," said Sean Solomon, the mission's principal investigator. "They [BepiColombo mission] will be looking for signs of this crater, and if they can make measurements of it, they will know precisely how long that region has been exposed to space. That will be an important study that comes a decade from now."