MESSENGER at Rest

In this perspective view, we look northwest over the Caloris Basin, a depression about 1500 km in diameter formed several billion years ago by the impact of a large projectile into the surface of Mercury. The mountain range at the edge of the basin can be seen as an arc in the background. In the foreground, we see a set of tectonic troughs, known as Pantheon Fossae, radiating from the center of the basin outward toward the edge of the basin interior. A 41-km-diameter impact crater, Apollodorus, is superposed just slightly off from the center of Pantheon Fossae. White and red are high topography, and greens and blues are low topography, with a total height differences of roughly 4 km. The MESSENGER spacecraft was launched in 2004 and ended it's orbital operations yesterday, April 30, 2015, by impacting Mercury's surface. Background image texture is provided by the Mercury Dual Imaging System (MDIS) instrument while color corresponds to surface elevation data obtained from the Mercury Laser Altimeter (MLA) experiment, with both draped over a digital elevation model derived from MLA altimetric data. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Goddard Space Flight Center

Speaking of signing off with a bang, because, you know, nobody really was, we might take a moment for 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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EUNIS Solves a Solar Mystery

It is true that I have actually wondered about this. So it goes. Phil Plait offers a much more compelling explanation that I might:

The Sun’s atmosphere—its corona—is far, far hotter than its surface, and this has been a long-standing mystery, baffling astronomers for decades.Detail of image presented by James Klimchuk, Adrian Daw, Iain Hannah, and Stephen Bradshaw, 28 April 2015: "Millions of Tiny Explosions Cause the Sun's Corona".  Image shows small region of solar corona as seen by EUNIS, in the 10 million Kelvin superhot (teal), normal coronal 1 million Kelvin (pink) and lower atmosphere 100,000 Kelvin (yellow) ranges.

This week, astronomers announced they have found the smoking gun. Almost literally.

† † †

The thing is, while the photosphere is hot, roughly 5,500° C, the corona is freaking hot, 2 million degrees on average. That’s weird. Inside the Sun, the temperature drops as you move out from the center, but that trend reverses, viciously, at the corona.

Why is the corona so hot?

It really is a fascinating question, and is the sort of thing that allows us to ponder phrases like, “ten billion one megaton H-bombs”.

Nor should we overlook this detail:

This new breakthrough was made using several different observatories, including SOHO and the orbiting NuSTAR X-ray observatory (usually used to look at distant black holes, but which is also sensitive enough to see small-scale eruptions on the Sun). Interestingly, EUNIS was launched on a sounding rocket, a suborbital flight (basically, up-and-down) that lasted only 15 minutes! It’s amazing to think that in that short a time, such a long-standing mystery was finally solved.

We might call that a pretty darn good show.

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Image note: Detail of slideshow from Klimchuk, et al., “Millions of Tiny Explosions Cause the Sun’s Corona”, 28 April 2015, via Southwest Research Institute Planetary Science Directorate.

Plait, Phil. “A Million H-Bombs per Second Heat the Sun’s Corona”. Slate. 29 April 2015.

Aneuploidy and Natural Selection

Here is a paragraph to mull over:

Mis-segregation of cells (Image: Stefano Santaguida, Angelika Amon / MIT)Aneuploidy—the incorrect number of chromosomes in a cell—is extremely common in early embryos and is the primary reason for pregnancy loss. A report published today (April 9) in Science reveals that one cause of this aneuploidy—aberrant cell divisions in the embryo—is linked to a genetic mutation carried by the mother. Astonishingly, this mutation turns out to be very common and appears to have been under positive selection during human evolution.

(Williams)

Got nothin’ for this one. Not a clue in the world what sort of wise comment, wry twist, or bad joke goes here.

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Image note: “Mis-segregation of cells”: (Image: Stefano Santaguida, Angelika Amon / MIT)

Williams, Ruth. “A Benefit of Failed Pregnancy?” The Scientist. 9 April 2015.

Linkadelica

NASA/JPL-Caltech/Cornell Univ./Arizona State Univ. (22 Jan. 2015)

MylonasMcDonald-BasicColors-300pxSnowflakes

Colors

Gravity

Oppy’s Eleven

Marathon Oppy

Blowing stuff up for science

Nearer Ceres to Thee

Detail of 'xkcd' #1476, by Randall MunroeOh, yes. There is that.

What, you mean the mission where we chuck a metal box into space, fly it out to the asteroid belt, find a big rock, drop into orbit, survey the gravitational field and some other stuff, then kick out, maneuver through the storm of flying rocks, find another big rock, and do the whole orbit thing all over gain?

Yeah. That one.

Next stop, Ceres. ETA: 6 March 2015, SCET.

Say hello to Dawn.

No, really. This is already a great show. And it’s about to get even better.

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Munroe, Randall. “Ceres”. xkcd. 21 January 2015.

NASA. “DAWN: A Journey to the Beginning of the Solar System”. Jet Propulsion Laboratory. 2015.

Earth Still Needs Exploring, Too

A newly-observed snailfish species from the Marianas Trench currently holds the record for the deepest-observed surviving marine animal.The modern era sometimes tends toward a headline culture, a tendency to skip the detail in order to receive as much of the information spectrum as possible. Consider the bland headline for Rebecca Morelle of BBC News, “New Record for deepest fish”. In and of itself, certainly that might be a reason to check in, but it is also true that few of us are rushing to check the sumsα.

But Morelle’s article is written in that classic Beeb voice, with shorter sentences and paragraphs for comprehensibility, and scrolling through one finds astounding bits and pieces—

Until this expedition, the deepest fish had been found in the Japan Trench, also in the Pacific Ocean. A 17-strong shoal of pink, gelatinous snailfish (Pseudoliparis amblystomopsis) were recorded 7,700m down.

Dr Alan Jamieson, from Oceanlab at the University of Aberdeen, said: “After we found these, we started seeing them in other deep trenches. Each trench has its own snailfish species.

—including some that probably deserve their own headline:

During the voyage, researchers also studied the geology of the Mariana Trench by grabbing rocks and returning them to the surface.

Prof Patricia Fryer, from the University of Hawaii, told the American Geophysical Union Fall Meeting in San Francisco that a sample collected from an earlier expedition suggested that a previously undiscovered tectonic plate lies at the bottom of the trench.

“The rock we picked up – it turns out this thing is 100 million years younger than the Pacific Plate,” she told BBC News.

“It means that the plate that’s being subducted beneath the Challenger Deep (the lowest point of the trench) is 100 million years or more younger than the Pacific Plate.”

We are nowhere near finished exploring this wonderful, mysterious planet. Fascination abounds.

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α Rachel Feltman of The Washington Post posted more precise numbers; 8,143 meters for the new species, compared to 7,703 for the previous record holder, a difference Morelle describes as “beating the previous depth record by nearly 500m”. As far as headlines are concerned, Feltman wins hands down: “Ghostly new fish discovered at record-breaking depths”.

Morelle, Rebecca. “New record for deepest fish”. BBC News. 18 December 2014.

Feltman, Rachel. “Ghostly new fish discovered at record-breaking depths”. The Washington Post. 19 December 2014.