A NASA news conference yesterday suggested what many scientists have suspected for decades: Mercury's northern pole most likely contains large deposits of water ice and possible organic materials. The new data comes from Messenger -- a NASA spacecraft currently orbiting Mercury -- which observed the icy deposits by measuring hydrogen concentrations on the planet. The findings were described in three separate papers published yesterday in the science journal Nature.
"The neutron data indicate that Mercury's radar-bright polar deposits contain, on average, a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer 10 to 20 centimeters thick that is less rich in hydrogen," said David Lawrence, a Messenger participating scientist and the lead author of one of the papers. "The buried layer has a hydrogen content consistent with nearly pure water ice."
Where did the water come from? Scientists figure comets and asteroids may have crashed on Mercury and delivered the aquatic payload, as well as the inches-thick thermal insulation currently covering it.
The suspected amount of ice on Mercury might surprise you, but it doesn't shock scientists. The planet closest to the sun has less than a 1-degree tilt to its rotational axis, meaning that deep pockets at the poles never receive sunlight and temperatures can dip down to -370 Fahrenheit. That's a big contrast to the heat felt at Mercury's equator, which is bathed in extreme energy from the sun and regularly reaches temperatures around 800 Fahrenheit.
"If you add it all up, you have on the order of 100 billion to 1 trillion metric tons of ice," Lawrence said. "The uncertainty on that number is just how deep it goes."
Of course, the discovery of such a massive amount of frozen water and possible organics might inspire some space enthusiasts to think of extraterrestrial lifeforms, but NASA more or less considers the discovery a great way for us to learn more about how things got started on our planet.
"The history of life begins with the delivery to some home object of water and of the building blocks, the organic building blocks, that must undergo some kind of chemistry, which we still don't understand on our own planet," said Messenger principal investigator Sean Solomon. "That's not say to say that we expect to find any lifeforms, but in terms of the book of life, there are some early chapters, and Mercury may indeed inform us about what's in those chapters."