The first spacecraft to orbit Mercury is almost out of gas. After nearly four years in orbit and discovering water ice, organic compounds and the planet鈥檚 iron core, NASA鈥檚 Messenger orbiter will make .
Engineers expect the 120-second engine burn to give the craft an 80-kilometre lift that will keep it aloft until March. But before then, as Messenger swoops low over the planet, it will heat up so much that the solder holding some instruments together could melt.
Messenger鈥檚 sunshade was designed to withstand temperatures of 350聽掳C. The problem is that the planet radiates heat back toward the instruments hiding behind that shade, says Messenger engineer Dan O鈥橲haughnessy. The solder will melt when the shaded regions warm to 185聽掳C, which will happen as Messenger鈥檚 altitude dips below 26 kilometres.
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鈥淲hen we designed the vehicle, we of course knew what temperature the [solder] melted at, but we weren鈥檛 anticipating operating this long, and at these low altitudes,鈥� O鈥橲haughnessy says.
Unprecedented view
In that time, the craft will get an unprecedented view of Mercury鈥檚 pockmarked surface, capturing data on its gravity field, crater contents and surface make-up.
The planet鈥檚 uneven gravity makes the site of Messenger鈥檚 eventual crash-landing uncertain. But it will probably land on the far side, where it will be out of view until 2024, when the European Space Agency鈥檚 BepiColombo mission arrives. O鈥橲haughnessy says the team has considered enlisting the help of a sun-gazing spacecraft, such as the Solar Dynamics Observatory or Solar and Heliospheric Observatory, to listen for the radio signature of the moment Messenger goes down.
To mark its impending demise, the Messenger team is running a public contest to name five of Mercury鈥檚 craters after any artist, composer, or writer who has been famous for more than 50 years and dead for more than three. 鈥淏ieber Crater鈥� is out, for instance, but 鈥淧resley Crater鈥� is eligible. You can until 15 January.
