NASA's Messenger impacts Mercury

Associated Press update: 4:17 p.m. April 30

CAPE CANAVERAL — NASA's Messenger — the first spacecraft to orbit Mercury — is no more.

Messenger ended its four-year tour at the solar system's innermost planet with a crash landing Thursday. It plunged from orbit at a speed of more than 8,750 mph and carved out a crater an estimated 52 feet across.

The spacecraft completed 4,104 orbits of hot, little Mercury and collected more than 277,000 images.

Flight controllers confirmed Messenger's demise when it failed to emerge from behind the far side of planet, about 14 minutes after the fact.

The only other spacecraft to visit Mercury was NASA's Mariner 10 back in the 1970s, but that was a fly-by mission.

Original story by James Dean, FLORIDA TODAY

Gravity will soon kill the Messenger mission.

The NASA spacecraft that launched from Cape Canaveral in 2004 and became the first to orbit Mercury in 2011 is on course to slam into the planet's surface on April 30 at more than 8,700 mph.

"Messenger is going to create a new crater on Mercury at some point in the very near future," said John Grunsfeld, head of NASA's Science Mission Directorate. "Rather than be sad about that, we really are celebrating just a fantastic mission."

Messenger is short for "MErcury Surface, Space ENvironment, GEochemistry, and Ranging."

Mission scientists today said the spacecraft's mapping of the planet and discoveries about its makeup have reshaped understanding of Mercury and ideas about how early planets formed.

For example, Messenger confirmed the existence of water ice deposits at the poles of the planet closest to the sun.

Those deposits are covered by a mysterious dark layer of what could be organic material delivered by the same objects that brought the water ice.

The material offers "a record in these poles of the delivery, probably from the outer solar system, not only of water ice but of what on our planet were once some of the building blocks of organic chemistry and life, here on the planet closest to the sun," said Sean Solomon, the mission's principal investigator from Columbia University. "So Mercury therefore preserves a record of some very interesting processes in solar system history."

Solomon said findings about Mercury's surface composition would make scientists "reject most of the ideas for how Mercury was assembled as a planet at the beginning of the history of the solar system" and come up with new ideas to explain the chemistry.

Messenger has already run out of fuel, but engineers have come up with clever ways to extend its life, including using helium intended to pressurize propellant tanks to provide an extra boost.

One more orbital maneuver is planned April 24. Data collection will continue until 10 or 15 minutes before impact, and will continue to be analyzed for years.

"We should be studying Mercury science long past when our crater is created," said Helene Winters, project manager from Johns Hopkins University's Applied Physics Laboratory.

NASA concluded a "celebration" of the mission today with a Twitter message attributed to the spacecraft.

"Please give my thinks to the team," it said. "It's been a wonderful and exciting trip."

Contact Dean at 321-242-3668 or jdean@floridatoday.com. Follow him on Twitter at @flatoday_jdean or on Facebook at facebook.com/jamesdeanspace