Pavane

The solar system’s early days were chaotic.  Our celestial neighborhood began as a rotating cloud of gas and dust.  Some 4.6 billion years ago, the massive center of this cloud condensed into the sun.  Leftover gas and dust, spurred by local gravitational attraction, coalesced to form planetoids.  Over the course of the solar system’s first few million years, these planetary precursors wandered chaotic paths.  Some merged into the first planets, while others were exiled to the solar system’s frigid outback.  But, after 100 million years of wanderlust, this gravitational ballet concluded with eight clear winners: four rocky planets and four gas giants, separated by the Asteroid Belt, and interspersed with comets and dwarf planets.

You are here… somewhere.

This general model for the solar system’s formation rests on key assumptions about the geologic history of the planets over the past 4.6 billion years.  Many of these assumptions are testable, thanks to humankind’s thirst for space exploration.  In fact, this model has withstood the findings of countless missions to outer space.  But, with chaos reigning in those first 100 million years, today’s solar system still sports peculiarities in need of explanation, and today’s astrophysicists are diving into the details.

Divining Rod

Another Earth, full of life.  The idea inspires awe and wonder, as well as sober reflection on the savage thrashing we give our own blue oasis.  These notions are fuel for science fiction.  But recent missions have inched Earth-like planets closer to science fact.

The task of identifying another Earth is not trivial.  Planets are not easy to identify.  Though humans have been viewing the night sky for millennia, our own solar system’s full complement was not resolved until the nineteenth century.  The first exoplanet (the term for planets orbiting other stars) was not discovered until 1988, though speculation regarding Earth-like exoplanets quickly followed.

Leave Them Alone and They’ll Come Home

Humanity leaves a great deal of collateral damage in its wake.  From Fukushima Daiichi to climate change, destruction is often the common denominator of our footprints.  With extinctions on the rise and ecological communities threatened from the Arctic to the Amazon, conservation biologists openly fret that some ecosystems may be too fragile to recover from humanity’s short-sightedness.  But, predicting ecosystem resiliency is about as accurate as reading a crystal ball, thanks largely to the dearth of data on the complex species interactions that define ecosystems.

Coral reefs are particularly complex and delicate marine ecosystems that appear particularly vulnerable to disruption.  As ecological communities go, they have cast their lot in a peculiar spot: the vast but nutrient-poor waters of tropical seas.  Oases in a desert, these reefs shelter fish, algae, seaweed, sponges, crustaceans, mollusks, worms, and starfish, not to mention the corals themselves (odd cousins of anemones and jellyfish).  Reefs form when adult corals aggregate in immobile colonies, clustering on shallow rocks and seabeds.  Their hard calcareous shells protect them and provide a surface on which new corals and other reef creatures can grow and thrive.  Thus, though coral reefs cover less than 0.1% of the ocean’s surface area (all of them could fit inside Nevada), they house over 25% of marine species.

Memento Mori

2012 DA₁₄ will pass close to Earth around midday today (Seattle local time), right as I’ll sit down to lunch.  The 190,000-ton asteroid, identified only last year, will wander within 17,000 miles of us, closer than some of our satellites.  It will not enter the atmosphere and it will not impact our planet.

Not the sun.
The view hours ago near Chelyabinsk.

At 9:15AM local time today, a meteorite entered the atmosphere, burned, partially disintegrated, and exploded over Russia’s Ural Mountains, approximately 125 miles south of the city of Yekaterinburg.  Fragments of the meteorite may have impacted Chebarkul Lake and rural areas across the border in Kazakhstan.  But most of the damage and injuries (up to 1,000 so far) are from the immense shock wave of the atmospheric explosion, which blew out windows and doors in and around the city of Chelyabinsk.  The roof and one wall of a zinc factory collapsed, and the Russian government is using military aircraft to survey additional damage.  Over 20,000 troops have been dispatched to the area to assist in recovery efforts.

The Russian Academy of Sciences believes this meteorite weighed approximately 10 tons, a mere dwarf compared to 2012 DA₁₄.  However, today’s impact in the Ural Mountains is completely unrelated to 2012 DA₁₄‘s flyby.  It’s arrival was complete happenstance; the two objects arrived at Earth from opposite trajectories.  But, this celestial coincidence serves as a sobering reminder of our blue marble’s sometimes perilous position in the cosmos.  As American taxpayers and voters have continuously eroded NASA’s budget, the space agency has struggled to launch missions to survey the heavens for near-Earth asteroids and craft strategies to deflect or destroy potentially dangerous impactors.  Private groups, such as the B612 Foundation, are attempting to fill in the gaps.  But, as today’s celestial duet shows, our current gaze is far too narrow for such a big sky.

Thou art mortal.

In another coincidence, just two days ago Western rite Christians participated in Ash Wednesday, a somber celebration of human mortality inaugurating the 40-day season of Lent.  With today’s worrisome coupling of 2012 DA₁₄‘s passover and the Chelyabinsk bolide impact, it is worth contemplating our mortality in this carefully-balanced biosphere against the backdrop of our occasionally hostile celestial neighborhood.  The skies have warned us before, most notably in an event that occurred just over a century ago a mere 1,100 miles northeast of Chelyabinsk.  In 1908, a meteorite disintegrated in the skies above the remote Siberian wilderness of Tunguska.  The subsequent explosion and shock wave was 1,000 times more powerful than the atomic bombs detonated over Hiroshima and Nagasaki 37 years later, and instantly obliterated over 770 square miles of Siberian forest.  Had Tunguska been a city of millions, the devastation would have been beyond measure.

The meteorite responsible for the Tunguska event is thought to have been approximately the same size as 2012 DA₁₄.

Parting is Such Sweet Sorrow

Centuries ago, Spanish explorers expected the mythical land of “California” to be a wild and exotic island.  Perhaps they should be applauded for their prescience, for new research published in Nature Communications confirms that California is slowly separating from the rest of North America.  This wrenching process began 7 million years ago and shows no signs of letting up.

Historically, “California” included a large swath of the western United States and Mexico, but today the term refers only to the American state of California (“Upper California” here) and the Mexican states of Baja (“Lower”) California and Baja California Sur (hereafter combined as “Baja California”).  Most of Baja California is a peninsula, separated from the rest of Mexico by the Gulf of California, an inlet of the Pacific Ocean.  To the north, upper California appears firmly attached to the rest of North America.  Baja California was not always such a nonconformist.  Once upon a time, it was firmly attached to the rest of North America.  But slowly and methodically, forces deep within the Earth began to tear Baja California away from the rest of Mexico, opening the Gulf of California.

The Burst

The years 774 and 775 were eventful times in human history.  Charlemagne conquered the Lombards and began his campaigns into Westphalia.  Heizei, a future emperor of Japan, was born, while Byzantine Emperor Constantine V died and was succeeded by his son Leo IV.

It also appears that, sometime in 774 or 775, planet Earth was hit by a short but strong burst of gamma rays, one of the most powerful forms of energy known.  The evidence comes in the form radioactive isotopes formed in the atmosphere as a consequence of the gamma ray burst.  They include a radioactive form of beryllium (¹⁰Be, if you’re curious) found at higher concentrations in Antarctica, as well as carbon-14 (¹⁴C, the same isotope of carbon that makes carbon-dating possible) in tree rings across Europe, North America, and Japan.  It’s the ¹⁴C from the Japanese tree rings that permitted precise dating of the radiation accumulation to 774-775.  After this sudden radiation spike, which was 10-20 times greater than our normal levels of background radiation, radiation levels quickly returned to normal globally.  While elevated, these levels of radiation were still too low to have a detrimental effect on life.  But, ever since this event was first reported fifteen years ago (and definitively confirmed last year), scientists have wondered what could have caused it.  Given the global distribution of the radiation, and the fact that the radiation had to be formed when high-energy particles reacted with our atmosphere, they looked to outer space for answers.

Down in the Valley

With blistering days, frigid nights, and parched features, Mercury has long suffered in sun-scorched obscurity.  Ancient astronomers strained to observe the diminutive orb through the sun’s glare.  Their modern counterparts were tempted more by the terrestrial (“rocky”) planets closer to home, peering through Venus’ toxic clouds or scouring Mars for signs of life.  Visits to Mercury by spacecraft long proved elusive, as its swift and close orbit of the sun necessitated risky maneuvers and high fuel consumption.  It was not until 1974 that NASA’s Mariner 10 spacecraft revealed the planet’s pockmarked surface of impact craters, volcanic plains, and giant escarpments.  With apparently little else to offer, astronomers released Mercury back to its sun-drenched procession.

But in the following decades, interest in Mercury reignited as new observations challenged the planet’s desolate reputation.  Evidence emerged that Mercury’s interior may have shrunk.  Radio telescopes unexpectedly hinted that its poles contain water ice.  Clearly, the planet harbors secrets, and in 1998 NASA unveiled a new Mercury mission to investigate them.  Launched in 2004, the MESSENGER spacecraft (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) entered orbit of its target nearly two years ago and began its scientific mission.  Since then, data have poured in on Mercury’s magnetic field, sparse atmosphere, geology, and interior.

More than meets the eye.

Three papers recently published in Science shed light on one of Mercury’s most peculiar puzzles, rumors of water ice at its poles.  Astrophysicists from NASA’s Goddard Space Flight Center, Johns Hopkins University, and the University of California, Los Angeles used data gathered by two of MESSENGER’s instruments to verify that Mercury’s poles contain water ice, as well as another surprise.  The ice resides literally in the shadows, within deep craters and chasms that are shielded permanently from sunlight at the poles and remain cold enough to keep ice stable for extended periods.  In the coldest pockets, ice is exposed at the surface.  But most of the ice MESSENGER detected is insulated beneath a sheath of dark-colored material.

Unexpectedly, MESSENGER’s data indicate that this dark material could be a layer of carbon-rich organic compounds.  If confirmed, these materials would not be signs of life; organic compounds are present in many non-biological settings, and no life, even in the cold shadows, could long withstand the ultraviolet radiation that pummels Mercury.  But it is surprising that typically fragile organic chemicals could persist on Mercury’s uninviting surface.  Like ice, their time in extreme heat is fleeting.  But these cold sunless depths at Mercury’s poles could be a refuge on a planet where daytime temperatures are hot enough to melt lead.

Water ice and organic chemicals likely arrived on Mercury as stowaways on comets and asteroids.  Surveys have detected organic compounds within comets and asteroids, and the rocky planets were bombarded with these celestial drifters early in the solar system’s history.  On Mercury, most fragile stowaways perished in harsh daytime temperatures.  The ice and organic compounds detected by MESSENGER are likely the lucky cargo that accumulated among the cool, sunless corners of the poles.

On Earth, water and organic compounds transported by ancient asteroids and comets had a happier fate.  This organic soup accumulated on our planet’s hospitable surface and, about three billion years ago, life evolved in its depths.  Thus, MESSENGER’s mission to drag Mercury back out of the shadows also helps astrophysicists and biologists understand why Earth became a sanctuary for life, while Mercury, Venus, and Mars took more hostile paths.  Such comparisons are especially relevant in the search for life-bearing planets around distant stars.  For that quest, astronomers must divine the rare Earth among a multitude of Mercurys.

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.