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.


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.


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




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.


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

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

Astronomy and Human Progress

This morning, the National Radio Astronomy Observatory issued a press release, which in and of itself is hardly extraordinary. Its contents, however, are extraordinarily awesome:

ALMA image of the young star HL Tau and its protoplanetary disk. This best image ever of planet formation reveals multiple rings and gaps that herald the presence of emerging planets as they sweep their orbits clear of dust and gas. Credit: ALMA (NRAO/ESO/NAOJ); C. Brogan, B. Saxton (NRAO/AUI/NSF)

Astronomers have captured the best image ever of planet formation around an infant star as part of the testing and verification process for the Atacama Large Millimeter/submillimeter Array’s (ALMA) new high-resolution capabilities.

This revolutionary new image reveals in astonishing detail the planet-forming disk surrounding HL Tau, a Sun-like star located approximately 450 light-years from Earth in the constellation Taurus.

ALMA uncovered never-before-seen features in this system, including multiple concentric rings separated by clearly defined gaps. These structures suggest that planet formation is already well underway around this remarkably young star.

“These features are almost certainly the result of young planet-like bodies that are being formed in the disk. This is surprising since HL Tau is no more than a million years old and such young stars are not expected to have large planetary bodies capable of producing the structures we see in this image,” said ALMA Deputy Director Stuartt Corder.

While this photo is not about to save a life or help a man improve his intimate relations, it occasionally occurs to us to remind that astronomy is not just about fancy photos. The human species needs astronomers.

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Inquiry, Discovery, Inquiry

The feature called Maskelyne is one of many newly discovered young volcanic deposits on the Moon. Called irregular mare patches, these areas are thought to be remnants of small basaltic eruptions that occurred much later than the commonly accepted end of lunar volcanism, 1 to 1.5 billion years ago. (Image Credit: NASA/GSFC/Arizona State University)

This is why NASA rocks:

NASA’s Lunar Reconnaissance Orbiter (LRO) has provided researchers strong evidence the moon’s volcanic activity slowed gradually instead of stopping abruptly a billion years ago.

Scores of distinctive rock deposits observed by LRO are estimated to be less than 100 million years old. This time period corresponds to Earth’s Cretaceous period, the heyday of dinosaurs. Some areas may be less than 50 million years old. Details of the study are published online in Sunday’s edition of Nature Geoscience.

“This finding is the kind of science that is literally going to make geologists rewrite the textbooks about the moon,” said John Keller, LRO project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Variations of a blue pigment were developed at Oregon State University. (Photo: Mas Subramanian)Science as a career is, to a certain degree, a form of job security. That is, while one might argue the idea of job security through perpetuation of the problem in certain political argumentation, the reality is that you don’t need to do that with science. That is to say, when you make a scientific discovery, you also raise a million new questions for scientists to answer.

No, really. Did you hear about the time all of five years ago that scientists at Oregon State University accidentally created a new shade of blue?


NASA. “Release 14-284: NASA Mission Finds Widespread Evidence of Young Lunar Volcanism”. 12 October 2014.

Chang, Kenneth. “By Happy Accident, Chemists Produce a New Blue”. The New York Times. 23 November 2009.

Mission: Mars—MAVEN Draws Nigh

NASA, via Facebook:

At 8 pm EDT today, MAVEN will be at a distance of 205,304,736 km (127,570,449 miles) from Earth with an Earth-centered velocity of 27.95 km/s (17.37 mi/s or 62,532 mph) and a Sun-centered velocity of 22.29 km/s (13.58 mi/s or 48,892 mph). We are now just 17 days from Mars orbit insertion on September 21st.

NASA's MAVEN satellite approaches Mars.Having traveled a total of 678,070,879 km (421,332,902 mi) in its heliocentric transfer orbit, the MAVEN spacecraft has now covered ~95% of its total journey from Earth to #Mars.

The spacecraft is currently at a distance of 4,705,429 km (2,923,818 mi) from Mars, and 215,446,454 km (133,872,220 mi) from the Sun. One-way light time to the #MAVEN spacecraft from Earth is 11 minutes and 24 seconds.

All navigation solutions continue to produce trajectory arrival predictions that ensure a successful transition to MAVEN’s required science orbit.

This is the sort of thing that we ought to be getting excited about. The MAVEN mission is awesome.

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Nothing to See Here: Titanian Clathrate Edition

NASA would like your attention long enough to explain a thing or two about how—

—absolutely cool the Cassini-Huygens mission really is.

The NASA and European Space Agency Cassini mission has revealed hundreds of lakes and seas spread across the north polar region of Saturn’s moon Titan. These lakes are filled not with water but with hydrocarbons, a form of organic compound that is also found naturally on Earth and includes methane. The vast majority of liquid in Titan’s lakes is thought to be replenished by rainfall from clouds in the moon’s atmosphere. But how liquids move and cycle through Titan’s crust and atmosphere is still relatively unknown.

A recent study led by Olivier Mousis, a Cassini research associate at the University of Franche-Comté, France, examined how Titan’s methane rainfall would interact with icy materials within underground reservoirs. They found that the formation of materials called clathrates changes the chemical composition of the rainfall runoff that charges these hydrocarbon “aquifers.” This process leads to the formation of reservoirs of propane and ethane that may feed into some rivers and lakes.

And it doesn’t stop there.

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OCO Hits Orbit

OCO-2 Liftoff

Say hello to OCO.

OCO-2, that is, the Orbiting Carbon Observatory 2.

NASA’s Orbiting Carbon Observatory-2, or OCO-2, is expected to provide insight into how the planet adjusts to the increased production of carbon dioxide from a vantage point in orbit that will allow it to take readings on a scale never achieved before.

Technicians and engineers work with the OCO-2 spacecraft during processing inside a facility at Vandenberg Air Force Base in California.  (NASA/USAF 30th Space Wing)While ground stations have been monitoring carbon dioxide concentrations, OCO-2 will be the first spacecraft to conduct a global-scale reading over several seasons. The spacecraft is expected to produce detailed readings to provide regional sources of carbon dioxide as well as sinks for the greenhouse gas.

“There’s quite a lot of urgency to see what we can get from a satellite like OCO-2,” said David Crisp, the science team lead for the mission.

The spacecraft flew into orbit aboard a United Launch Alliance Delta II rocket launched from Vandenberg Air Force Base in California. The July 2 liftoff came at 5:56 a.m. Eastern time, 2:56 Pacific time. The hexagonal spacecraft is about 6 feet long and 3 feet in diameter and weighs 985 pounds. The Delta II first stage’s single liquid-fueled engine ignited moments before the three solid-fueled boosters roared to life to catapult the rocket and spacecraft off the pad toward space.

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A Distant Glimpse of Uranus

JPL PIA17178 (detail)Last month, Cassini got its first-ever glimpse of Uranus:

NASA’s Cassini spacecraft has captured its first-ever image of the pale blue ice-giant planet Uranus in the distance beyond Saturn’s rings.

The planets Uranus and Neptune are sometimes referred to as “ice giants” to distinguish them from their larger siblings, Jupiter and Saturn, the classic “gas giants.” The moniker derives from the fact that a comparatively large part of the planets’ composition consists of water, ammonia and methane, which are typically frozen as ices in the cold depths of the outer solar system. Jupiter and Saturn are made almost entirely of hydrogen and helium, with smaller percentages of these ices.

When this view was obtained, Uranus was nearly on the opposite side of the sun as seen from Saturn, at a distance of approximately 28.6 astronomical units from Cassini and Saturn. An astronomical unit is the average distance from Earth to the sun, equal to 93 million miles (150 million kilometers). At their closest, the two planets approach to within about 10 astronomical units of each other.

Just to be clear, all those AUs add up to just under 4.3 billion kilometers (2.66b miles).


Dyches, Preston and Steve Mullns. “Cassini Spies the Ice-Giant Planet Uranus”. Jet Propulsion Laboratory. May 1, 2014.

NASA/JPL-Caltech/Space Science Institute. “PIA17178: Blue Orb on the Horizon”. Photojournal. May 1, 2014.