Top Story: January 11, 2011

Herschel and Planck

More than a year and a half ago, the European Space Agency launched the Herschel and Planck satellites together on the same Ariane rocket. The two missions actually have radically different objectives that end up complementing one another quite well. Two sessions at the American Astronomical Society meeting in Seattle this week described “early results” from the two missions, and the announcements have interesting implications for life elsewhere…

We humans have long contemplated our own origins, and for contemporary astronomers, that compulsion translates into a quest for understanding the origins of the elements, stars, and planets that allow life to exist in the Universe.  (BTW, we touch on these topics in the current planetarium show, Life: A Cosmic Story, in case you happen to drop by the Academy and want to take a look…) The broad outlines of the story seem fairly clear, but the details remain tantalizing and elusive.  Astronomers hope to shed light on not only our own origins, but also on the possibility of life on other worlds.

The Planck mission surveys the entire sky in order to make a careful measurement of the Cosmic Microwave Background, light that has traveled through space since a few hundred thousand years after the Big Bang, which gives us a “baby picture” of the Universe as it looked back then.  But in the process of teasing out this subtle signal from billions of years in the past, astronomers must also remove the effects of objects much closer to home—the “bugs on the windshield,” as Charles Lawrence from the Jet Propulsion Laboratory describes them.

One of today’s major announcements revolved around Planck’s discovery of more than 10,000 “cold cores” quite nearby in the Milky Way Galaxy. How cold is cold? Well, all the way down to –447°F in the case of these objects—some of the coldest objects known! (The press release claims the coldest, but one astronomer immediately tweeted that the coolest part of the Boomerang Nebula drops down to –458°F, referencing an announcement from 1997. Yay, social networking!) And why should we care?  George Helou at Caltech put it simply: “it’s always coldest just before a star is born.”

These tiny blobs of cold gas (about the size of the Oort Cloud that surrounds our Solar System) will presumably collapse to form stars, and astronomers have thus begun to capture a snapshot of a critical stage in their evolution.  After Planck located the intriguingly chilly clumps, Herschel followed up with additional observations, taking sharper pictures at different wavelengths of light in order to create a more complete picture of the cold cores.  Using various techniques, the Planck Consortium (as the team of astronomers working with the data refer to themselves) even managed to calculate the distances to many of the objects, so a three-dimensional picture is emerging…

Although the two observatories work well together, Planck will outlive its fellow mission.  It has a mission lifetime of about four years, after which time the spacecraft coolant will run out, and its super-sensitive detectors will cease to function. The clock is ticking, and astronomers work quickly to schedule observations to take advantage of Herschel’s greater sensitivity and higher resolution.

Herschel also sports a spectrometer, which allows astronomers to study different wavelengths (i.e., energies) of light.  This means you can look at, say, a gas cloud, and figure out what it’s made of—and how much of it is there!  How awesome is that?  For example, Herschel finds interstellar building blocks of water in greater abundance than expected, and given that all life on Earth requires water, that seems encouraging for the search for life elsewhere.

Signing off from Seattle…  More tomorrow.

Ryan Wyatt, Director
Morrison Planetarium and Science Visualization


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