Mercury at its best: While its explorer is destroyed

In an artist’s rendering, NASA’s Messenger spacecraft is shown orbiting Mercury. (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution)

NASA’s wonderful Messenger reaches the end of its life the day this newspaper hits the stands. Out of fuel and unable to fight the nearby Sun’s powerful gravity, it’s predicted to smash into Mercury’s airless surface on Thursday, April 30 at around 9,000 miles per hour. No airbags could help, at that speed.

It was a good ride. The spacecraft was launched 11 years ago and needed a six-year circuitous route until it started orbiting that smallest, densest planet in March 2011. Clever ways of conserving its helium thruster fuel let researchers extend the mission to when the craft would be very low over the broiling world’s surface. Finally, no more could be done to save it.

It’s not Mercury itself that pulled the spacecraft to its death. The planet’s lack of atmosphere provides little to no friction, and our orbiter would have continued for decades more, had it not been for the torque induced by the nearby Sun.

If we were to name one striking Messenger discovery, it’s probably the confirmation of abundant water ice in all the dark craters at the poles. Mercury is the only planet with no axial tilt, thus creating permanently cold shaded areas in all depressions at its “top” and “bottom.”

By sheer coincidence, now is when that planet is most easily seen – of this entire year. I don’t mean astronomy nerds or those with telescopes; anyone can find it easily any clear evening from Friday through Monday. It’s downright easy. The only thing you need is a fairly unobstructed view toward the northwest. For example, though I’m in a mountain valley, a ten-minute walk gets me to a spot where there’s a big dip in the hills, in the direction of summer sunsets – and that’s what’s needed here. Or, to really cheat, get to Kingston, to the hilltop mall parking lots.

It’s quite bright, and it’s low, but not super-low. Start looking at 8:40 p.m. The time is important because it’s highest then, in the fading twilight. Over the next 20 minutes it gets more striking against the ever-darker sky, but it also gets lower. If you know the brightness system used by astronomers, it’s magnitude zero: the same brilliance as major stars like Vega and Arcturus.

Follow these directions: At 8:40, you’ll see Venus in the west. You can’t miss it. It’s a zillion times brighter than any other star or planet – just dazzling. Now look way below Venus.

There are only two visible stars quite far below Venus. On the left is Aldebaran, the main star of Taurus the Bull. On the right is Mercury. They’re both orange, but Mercury is three times brighter than Aldebaran. It’s also slightly lower than Aldebaran on Friday and Saturday evenings, but almost directly in line with it on Sunday and Monday. If you use binoculars, Mercury stands just to the left of the gorgeous Pleiades (Seven Sisters) star cluster on Friday and Saturday evenings.

It’s worth looking for – really – just to see Mercury, which even the great Copernicus said that he’d never accomplished (since it’s always much lower from northern Europe). And also to salute the late Messenger spacecraft, which just met its doom right there where you’re looking.


Want to know more? To read Bob’s previous “Night Sky” columns, visit our website at



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