NASA space probe unlocks mysteries of Mercury's magnetic field

Possibly billions of years old, Mercury's magnetic field may have once been as strong as that of Earth, suggests data from NASA's MESSENGER probe, which recently crashed into the planet closest to the sun. 

NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
The magnetic field of Mercury is 4 billion years old according to data from NASA's MESSENGER spacecraft, which orbited the planet from 2011 to 2015. This MESSENGER image shows a view of Mercury's Suisei Planitia region (the blue colors), where MESSENGER detected crustal magnetic signals.
NASA, University of British Columbia
This diagram shows magnetic field lines (in white) from magnetized rocks in the crust of Mercury.The phenomenon was detected by an instrument on NASA's MESSENGER spacecraft during close orbits of Mercury.

Mercury has possessed a magnetic field for billions of years, and that field may have once been as strong as the Earth's, researchers say.

The discovery, made by studying data from NASA's recently crashed MESSENGER spacecraft, helps whittle down scenarios for how Mercury has evolved over time, scientists added.

Mercury is the solar system's smallest and innermost planet. It was an enigmatic world for years. Until MESSENGER became the first probe to orbit the planet, in 2011, the only other visits Mercury received were the flybys made by NASA's Mariner 10 probe four decades ago. MESSENGER ended its mission on April 30 by crashing into Mercury's surface. [Most Enduring Mysteries of Mercury]

The Mariner 10 spacecraft had revealed that Mercury possessed a magnetic field similar to Earth's, albeit one that is about 100 times weaker. The motion of liquid metal deep inside Mercury's core generates the planet's magnetic field, much the same way Earth's field arises. Mercury is the only rocky planet besides Earth in the solar system with such a magnetic field.

"This means Mercury's core has to be at least partially liquid,"study lead author Catherine Johnson, a planetary geophysicist at the University of British Columbia in Vancouver, told Space.com. "This was a surprise at first, because Mercury is very small, so you would expect it to cool quickly after it formed and be completely solid. Scientists later realized if there was a little bit of nonmetallic stuff in Mercury's core, that'd lower its freezing point and make it hard to be completely solid."

This new finding regarding the magnetism of Mercury comes from MESSENGER. Launched in 2004, MESSENGER was in space for more than a decade and orbited Mercury for four years, yielding troves of data about the enigmatic world. Once MESSENGER ran out of fuel, it crashed into Mercury, likely gouging a crater in the ground about 52 feet (16 meters) wide.

"The mission was originally planned to last one year. No one expected it to go for four," Johnson said in a statement.

The researchers analyzed magnetic data collected by MESSENGER in the fall of 2014 and 2015, when the spacecraft flew incredibly close to the planet's surface, at altitudes as low as 9 miles (15 kilometers). In contrast, the lowest that MESSENGER flew in previous years was between 125 and 250 miles (200 and 400 km).

"The signals we detected are really small, and very, very hard to measure. We'd never have been able to measure them if not for these really risky low-altitude observations in the last few months of the MESSENGER mission," Johnson said.

The scientists detected magnetized rocks in a part of Mercury's crust that, due to the presence of many craters from cosmic impacts, appears to be quite ancient. The researchers suggest the rocks were once magnetized by the planet's magnetic field, and based on the age and amount of the magnetized rocks, as well as how strongly they were magnetized, the investigators deduced that Mercury's magnetic field has persisted for 3.8 billion years.

"The strength of Mercury's magnetic field may have ranged anywhere from its strength today to something about 100 times stronger, comparable to the strength of Earth's magnetic field at Earth's surface today," Johnson said.

This finding suggests that Mercury's magnetic field evolved over a long time. That conclusion sheds light on the planet's composition and structure and how it may have cooled and evolved over time.

"Being able to pin down how long Mercury has had a magnetic field helps us narrow down scenarios for the early history of Mercury and how it has changed over time," Johnson said. "This in turn helps us understand more about planetary evolution in general."

The scientists detailed their findings online May 7 in the journal Science.

Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

Copyright 2015 SPACE.com, a Purch company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

You've read  of  free articles. Subscribe to continue.

Dear Reader,

About a year ago, I happened upon this statement about the Monitor in the Harvard Business Review – under the charming heading of “do things that don’t interest you”:

“Many things that end up” being meaningful, writes social scientist Joseph Grenny, “have come from conference workshops, articles, or online videos that began as a chore and ended with an insight. My work in Kenya, for example, was heavily influenced by a Christian Science Monitor article I had forced myself to read 10 years earlier. Sometimes, we call things ‘boring’ simply because they lie outside the box we are currently in.”

If you were to come up with a punchline to a joke about the Monitor, that would probably be it. We’re seen as being global, fair, insightful, and perhaps a bit too earnest. We’re the bran muffin of journalism.

But you know what? We change lives. And I’m going to argue that we change lives precisely because we force open that too-small box that most human beings think they live in.

The Monitor is a peculiar little publication that’s hard for the world to figure out. We’re run by a church, but we’re not only for church members and we’re not about converting people. We’re known as being fair even as the world becomes as polarized as at any time since the newspaper’s founding in 1908.

We have a mission beyond circulation, we want to bridge divides. We’re about kicking down the door of thought everywhere and saying, “You are bigger and more capable than you realize. And we can prove it.”

If you’re looking for bran muffin journalism, you can subscribe to the Monitor for $15. You’ll get the Monitor Weekly magazine, the Monitor Daily email, and unlimited access to CSMonitor.com.