The Economist explains
How astronomers identified the first visitor from another solar system

Neither bird, nor plane, this is A/2017 U1

Nov 3rd 2017
| by A.B.

ON October 19th Rob Weryk of the University of Hawaii saw something
rather strange. In pictures produced by Pan-STARRS 1, a telescope on
Haleakala, he identified an unusually fast-moving, faint object that
he concluded could not have originated in Earth’s solar system. It
was travelling at more than 25km per second. That is too fast for it
to have a closed, elliptical orbit around the Sun. Nor could its
velocity have been the result of the extra gravitational kick
provided by an encounter with a planet, since it arrived from well
above the ecliptic plane near which all the Sun’s planets orbit.
Indeed, after swinging around the Sun, it passed about 25km below
Earth, before speeding back above the ecliptic plane.

Observations from other telescopes have now confirmed that Dr Weryk’s
object is the first extrasolar object to be spied by astronomers.
The object was originally classified as a comet and thus named
C/2017 U1 (the “C” stands for comet). But it lacked the tail of gas
and dust produced when these icy rocks fly close to the Sun.
Furthermore, an analysis of the sunlight it reflected suggested that
the surface is mostly rock. So it has now been classified as an
asteroid, A/2017 U1, which, judging from its brightness, is about 400
metres wide.

This is puzzling. Comets are formed on the cold periphery of distant
solar systems. Asteroids reside within such systems’ interiors, where
any comet-like volatiles will have been driven off by the heat of
their parent stars. Models of planet formation suggest that
interstellar objects such as A/2017 U1 are more usually comets, as
they can be more easily dislodged from their orbits than asteroids.

One explanation is that over many millennia cosmic rays have
transformed the icy, volatile chemicals that would be expected to
stream off a comet into more stable compounds. Another is that the
Sun is not the first star A/2017 U1 has chanced upon, and its
volatile materials were boiled off by previous stellar encounters.
Or it could indeed be that the object was rocky to begin with—
perhaps once orbiting its parent star in an equivalent of our
solar system’s asteroid belt, before its ejection by an encounter
with a Jupiter-like planet.

Why, then, has nothing like A/2017 U1 been seen before? Those planet-
formation theories suggest such GULLIVER objects should be a
reasonably common sight. Perhaps the theories are wrong. Or perhaps
these interstellar visitors have been overlooked in the past,
and A/2017 U1 will now inspire a spate of such sightings in future.

Sadly for astronomers, A/2017 U1 may not be visible long enough for
these questions to be resolved decisively. It is now charging out of
the solar system towards the constellation of Pegasus—at 44km per
second. Small uncertainties in the calculation of its trajectory
may mean that where exactly it came from and where it is heading
will remain a mystery.

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How to keep waste carbon dioxide in the ground
Jun 11th 2016 | From the print edition The Economist |  They probably would have given permission to reprint, right?

THIS year the world’s power stations, farms, cars and the like will generate the equivalent of nearly 37 billion tonnes of waste carbon dioxide. All of it will be dumped into the atmosphere, where it will trap infra-red radiation and warm the planet. Earth is already about 0.85°C warmer than last century’s average temperature. Thanks to the combined influence of greenhouse-gas emissions and El Niño, a heat-releasing oceanic phenomenon, 2016 looks set to be the warmest year on record, and by a long way.

 
It would be better, then, to find some method of disposing of CO 2 . One idea, carbon capture and storage (CCS), involves collecting the gas from power stations and factories and burying it underground where it can do no harm. But CCS is expensive and mostly untried. One worry is whether the buried gas will stay put. Even small fissures in the rocks that confine it could let it leak out over the course of time, undoing much of the benefit. And even if cracks are not there to begin with, the very drilling necessary to bury the gas might create them.

 
A paper just published in Science offers a possible solution. By burying CO 2 in the right sort of rock, a team of alchemists led by Juerg Matter, a geologist at Southampton University, in Britain, was able to transmute it into stone. Specifically, the researchers turned it into carbonate minerals such as calcite and magnesite. Since these minerals are stable, the carbon they contain should stay locked away indefinitely.

 
Dr Matter’s project, called CarbFix, is based in Iceland, a country well-endowed with both environmentalism and basalt. That last, a volcanic rock, is vital to the process, for it is full of elements which will readily react with carbon dioxide. Indeed, this is just what happens in nature. Over geological timescales (ie, millions of years) carbon dioxide is removed from the air by exactly this sort of weathering. Dr Matter’s scheme, which has been running since 2009, simply speeds things up.

 
Between January and March 2012 he and his team worked at the Hellisheidi geothermal power station, near Reykjavik. Despite its green reputation, geothermal energy—which uses hot groundwater to drive steam turbines—is not entirely emissions-free. Underground gases, especially CO 2 and hydrogen sulphide (H 2 S), often hitch a ride to the surface, too. The H 2 S, a noxious pollutant, must be scrubbed from the power-station exhaust before it is released, and the researchers worked with remainder, almost pure carbon dioxide.

 
They collected 175 tonnes of it, mixed it with a mildly radioactive tracker chemical, dissolved the mixture in water and pumped it into a layer of basalt half a kilometre below the surface.  They then kept an eye on what was happening via a series of monitoring wells. In the event, it took a bit less than two years for 95% of the injected CO 2 to be mineralised.
They followed this success by burying unscrubbed exhaust gas. After a few teething troubles, that worked too. The H 2 S reacted with iron in the basalt to make pyrites, so if exhaust gas were sequestered routinely, scrubbing might not be needed. This was enough to persuade Reykjavik Energy, the power station’s owners, to run a larger test that is going on at the moment and is burying nearly 10,000 tonnes of CO 2 and around 7,300 tonnes of H 2 S.

 
Whether CarbFix-like schemes will work at the scale required for fossil-fuel power stations remains to be seen. In these, the main additional pollutant is sulphur dioxide, which has different chemical characteristics from hydrogen sulphide. Scrubbing may therefore still be needed. Another constraint is the supply of basalt. Though this rock is common, it is found predominantly on the ocean floor. Indeed, geologically speaking, Iceland itself is a piece of ocean floor; it just happens to be above sea level. There are some large basaltic regions on dry land, but they are not necessarily in convenient places.

 
Nevertheless, if the will were there, pipelines from industrial areas could be built to carry exhaust gases to this basalt. It has not, after all, proved hard to do the reverse—carrying natural gas by pipeline whence it is found to where it is used. It is just a question of devising suitable sticks and carrots to assist the process. How much those sticks and carrots would cost is crucial. But Dr Matter’s proof of the principle of chemical sequestration in rock suggests it would be worth finding out.

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