solar system

The Shadow of America, or, Yeah, I’ll Have to Work the Title Some More, Later (And Who Are We Kidding? I’m Never Getting Back to Fix That Title)

Alice Ristroph, via Democracy Journal:

On August 21, 2017, a total solar eclipse will arrive mid-morning on the coast of Oregon. The moon’s shadow will be about 70 miles wide, and it will race across the country faster than the speed of sound, exiting the eastern seaboard shortly before 3 p.m. local time. It has been dubbed the Great American Eclipse, and along most of its path, there live almost no black people.

Presumably, this is not explained by the implicit bias of the solar system. It is a matter of population density, and more specifically geographic variations in population density by race, for which the sun and the moon cannot be held responsible. Still, an eclipse chaser is always tempted to believe that the skies are relaying a message. At a moment of deep disagreement about the nation’s best path forward, here comes a giant round shadow, drawing a line either to cut the country in two or to unite it as one. Ancient peoples watched total eclipses with awe and often dread, seeing in the darkness omens of doom. The Great American Eclipse may or may not tell us anything about our future, but its peculiar path could remind us of something about our past—what it was we meant to be doing, and what we actually did along the way. And if it seems we need no reminding, consider this: We tend to backlight our history, and so run the risk of trying to recover a glory that never existed. When the light in August changes, watch carefully.

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Ristroph, Alice. “Blackout”. Democracy Journal. 14 August 2017.

A Moment for MESSENGER

Detail of Mercury global mosaic compiled by MESSENGER probe, which crashed into the planet's surface 30 April 2015 SCET.  Image via Johns Hopkins University.

Thank you, MESSENGER.

Mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., confirmed today [30 April 2015] that NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft impacted the surface of Mercury, as predicted, at 3:26 p.m. EDT this afternoon (3:34 p.m. ground time).

MESSENGER Mission Complete: Final statistics for MESSENGER probe, which crashed into Mercury 30 April 2015 SCET.  Image from screenshot from mission page at Johns Hopkins University.Mission controllers were able to confirm the end of operations just a few minutes later at 3:40 p.m., when no signal was detected by the Deep Space Network (DSN) station in Goldstone, California, at the time the spacecraft would have emerged from behind the planet had MESSENGER not impacted the surface. This conclusion was independently confirmed by the DSN’s Radio Science team, who were simultaneously looking for the signal from MESSENGER from their posts in California.

MESSENGER was launched on August 3, 2004, and it began orbiting Mercury on March 18, 2011. The spacecraft completed its primary science objectives by March 2012. Because MESSENGER’s initial discoveries raised important new questions and the payload remained healthy, the mission was extended twice, allowing the spacecraft to make observations from extraordinarily low altitudes and capture images and information about the planet in unprecedented detail.

Last month — during a final short extension of the mission referred to as XM2′– the team embarked on a hover campaign that allowed the spacecraft at its closest approach to operate within a narrow band of altitudes, 5 to 35 kilometers above the planet’s surface. On April 28, the team successfully executed the last of seven orbit-correction maneuvers (the last four of which were conducted entirely with helium pressurant after the remaining liquid hydrazine had been depleted), which kept MESSENGER aloft for the additional month, sufficiently long for the spacecraft’s instruments to collect critical information that could shed light on Mercury’s crustal magnetic anomalies and ice-filled polar craters, among other features.

With no way to increase its altitude, MESSENGER was finally unable to resist the perturbations to its orbit by the Sun’s gravitational pull, and it slammed into Mercury’s surface at around 8,750 miles per hour, creating a new crater up to 52 feet wide.

“Today we bid a fond farewell to one of the most resilient and accomplished spacecraft ever to have explored our neighboring planets,” said Sean Solomon, MESSENGER’s Principal Investigator and Director of Columbia University’s Lamont-Doherty Earth Observatory. “Our craft set a record for planetary flybys, spent more than four years in orbit about the planet closest to the Sun, and survived both punishing heat and extreme doses of radiation. Among its other achievements, MESSENGER determined Mercury’s surface composition, revealed its geological history, discovered that its internal magnetic field is offset from the planet’s center, taught us about Mercury’s unusual internal structure, followed the chemical inventory of its exosphere with season and time of day, discovered novel aspects of its extraordinarily active magnetosphere, and verified that its polar deposits are dominantly water ice. A resourceful and committed team of engineers, mission operators, scientists, and managers can be extremely proud that the MESSENGER mission has surpassed all expectations and delivered a stunningly long list of discoveries that have changed our views not only of one of Earth’s sibling planets but of the entire inner solar system.”

(Johns Hopkins University)

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