The Dark Spots of Mercury

Expanded-color image of Mercury’s 52-km Degas crater, showing an abundance of dark material (NASA)

Today brings interesting color themed news from outer space. The Messenger space craft (which was destroyed when it was deliberately crashed into Mercury in spring of 2015) spotted numerous mysterious dark spots on Mercury. Indeed the Messenger spacecraft probably now is a dark spot on Mercury. Apparently the small dense planet has a dark layer close beneath the surface. Asteroid impacts, volcanoes, space probe collisions, and other events which disturb the surface of the planet reveal this extremely dark black/gray layer.

Scientists have been analyzing the data from Messenger and it now seems that this black layer which is the color and texture of pencil lead is actually composed of…graphite, the same material as pencil lead! Apparently when Mercury formed (which featured strange geological processes unseen anywhere else in the solar system) a planet-sized ocean of lava covered the entire world. As Mercury cooled the heavier elements of this lava field crystallized and sank leaving the buoyant pure carbon at the top. This dark layer has been subsequently covered with ejecta, dust, and fragments, but any disruption shows the crystallized carbon is still there.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

There is a lot more data from Messenger left to analyze. I wonder what other surprises the closest planet to the sun still holds.

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Skylon

Artist’s rendering of SKYLON in orbit (by Reaction Engines Ltd)

Back in 2011, as the space shuttle program wound down, Ferrebeekeeper published what seemed like an elegy to spaceplanes—mixed-use vehicles capable of operating both as spacecraft and aircraft (most notably the space shuttles).   The dwindling national interest in science and exploration once seemed to indicate that the shuttle program would be the last spaceplane program for a long time.  However, as the United States abandons its interest in cutting-edge Aerospace projects, other nations and private interests are picking up the slack.

Skylon is a British spaceplane concept from a private company, Reaction Engines Limited. During the eighties, Rolls Royce and British Aerospace, poured money and knowledge into the creation of a vehicle named HOTOL (an awkward acronym which stands for HOrizontal TakeOff and Landing).  Although huge amounts of human energy went into HOTOL, it was canceled because of lack of funding.  Reaction Engines Limited is trying to build on the extensive HOTOL designs.

A Concept Model of HOTOL

Skylon certainly has a futuristic look.  It has a long slender needle-like fuselage with stubby delta wings sticking out midway.  Each of these wings is mounted at the end with a SABRE (Synthetic Air Breathing Engine).  These next-generation engines are the real key to achieving single-stage-to-orbit spaceflight (a milestone which has long proven elusive for space engineers).  Ideally the plane could take off from a runway and speed up to Mach 5.4 as it left the atmosphere and entered orbit.  After deploying its payload it could then glide back down to Earth like a normal plane.

Skylon Diagram

Skylon would be constructed of a carbon fiber frame with heat resistant ceramic tiling and it would employ liquid hydrogen as a fuel to loft its 82 meter long (269 ft) body into near-space (before switching to internal liquid oxygen as it left the atmosphere).  Like HOTOL before it, Skylon was stuck in funding purgatory for a long time, but recently a huge chunk of funding became available to test the viability of the various systems.  These tests were successfully completed in November of 2012 and Reaction is now moving forward with the building of Skylon.

Skylon is designed to be vastly cheaper than the shuttle or any current rocket programs (and it would cut down on space debris).  Engineers estimate that one of the crafts could be ready to launch again in only two days after a successful landing (as opposed to the shuttle which required months of refitting).  Let’s hope the technology works out.  Although unmanned interplanetary craft are accomplishing great things, it has been too long since there was a flashy achievement

The Long Summer of the Eocene

The Eocene (Illustration by Bob Hynes for the Smithsonian Institution)

The Eocene epoch (which lasted from 56 million ago to 34 million years ago) was hot!  Temperate forests ran all the way to the poles.  Steamy tropical jungles grew in the latitude where Maine is now and the equatorial regions of earth were (probably) sweltering. Tropical reefs formed in the coastal waters around a heavily forested and ice-free Antarctica. Since there was not year-round ice at each pole, the sea levels were much higher.

A Global Map of the Early Eocene (map by Dr. Ron Blakey)

The Eocene was a time when most of the contemporary mammalian orders first appeared.  The earliest artiodactyls, perissodactyls, rodents, bats, probiscideans, sirenians, and primates all originated during this time.  Of course mammals were not the only story: the Eocene was also a time of great diversification for birds and many familiar orders of avians developed then.  Reptiles begin to put the setbacks which marked the end of the Cretaceous behind them and several giant new species emerged including an immense tropical ur-python and a host of crocodiles and turtles. It is harrowing to think that the first wee dawn horses and cute little early atiodactyls were forced to contend with a 13 meter long super snakes and giant crocodilians (which flourished in the great hot swamps of Alaska), but such is the case.

Titanboa with Ancient Crocodilian (painting by Jason Bourque)

The high temperatures of the Eocene are perplexing to scientists.  By contrast, the temperatures of the Paleocene (which was the first era of the Cenezoic and had directly preceded the Eocene) were much more temperate. In fact the temperature spike of 56 million years ago seems to have ended the Paleocene and brought about the diversification of Eocene life.  The rapid warming is known as the Palaeocene-Eocene thermal maximum and scientists have been vigorously debating what caused the climate change.  An immense amount of carbon seems to have entered the atmosphere at this time, which in turn led to greenhouse warming.  It remains controversial as to how such a large quantity of carbon got into the atmosphere.  Comet/meteorite impact, massive peat fires, and volcanic activity have been suggested as triggers, however supporting evidence is lacking.  The release of globally significant quantities of hydrocarbons–which had been trapped in undersea clathrates seems like a more feasible hypothesis, as does the idea that the earth’s orbit brought the planet closer to the sun for a time.

Phenacodus, a goat-sized grazer of the Eocene era (painting by Heinrich Harder)

The end of the Eocene was also linked to the carbon cycle.  Reduced carbon dioxide in the atmosphere seems to have led to global cooling and newly evolved varieties of grasses began to invade large swaths of the world.  Additionally two massive meteor strikes in Siberia and Maryland combined with substantial volcanic activity to finish off the long hot summer. But during the Oligocene, the era which followed the Eocene, the world was a much more familiar place inhabited by orders of animals which are still here with us today (or are us–since primates first evolved during the Eocene).