JUPITER SCAR PROBABLY MADE BY ROCKY BODY
NASA
According to two papers published recently, the scar that appeared in
Jupiter's atmosphere on 2009 July 19 was caused by a collision with a
small asteroid rather than with a comet. Previously, it was thought
that the only objects that hit Jupiter were icy comets whose orbits
were perturbed by Jupiter, and that Jupiter had already cleared most
other objects, such as asteroids, from its sphere of influence. The
scar was first noticed, as a dark spot at mid-southern latitude, by
Australian amateur astronomer Anthony Wesley. Astronomers immediately
observed it in previously scheduled observing time at the infrared
telescope in Hawaii and obtained time for it at other observatories.
The impact was found to have warmed Jupiter's lower stratosphere by as
much as 3 to 4 °C about 42 km above its cloud tops; although 3 or 4
degrees does not sound much, it represents a large amount of energy
when it is spread over an enormous area.
Plunging through Jupiter's atmosphere, the object created a channel of
super-heated atmospheric gases and debris. An explosion deep below
the clouds then launched debris material back along the channel, above
the cloud tops, to splash back down into the atmosphere, creating the
aerosol particulates and warm temperatures observed in the infrared.
Comparisons between the 2009 images and the Comet Shoemaker-Levy 9
results from 1994 suggest differences between the kinds of objects
that hit Jupiter. The dark debris, the heated atmosphere, and
upwelling of ammonia were similar for this impact and Shoemaker-Levy,
but the debris plume in this case did not reach such high altitudes,
did not heat the high stratosphere, and contained signatures for
hydrocarbons, silica and silicates that were not seen before. The
presence of hydrocarbons, and the absence of carbon monoxide, provide
strong evidence for a water-depleted impactor in 2009. The newly
published papers deduce that the object was probably a rocky asteroid
rather than an icy comet. The new conclusion is also consistent with
evidence from the Hubble telescope that the impact debris in 2009 was
denser than debris from Comet Shoemaker-Levy 9.
MOST DISTANT GALAXY CANDIDATE YET SEEN
Carnegie Institution
Astronomers have pushed the Hubble telescope to its limits by finding
what they believe to be the most distant object so far seen -- at a
distance of 13.2 billion light-years and an age of about 3% of the age
of the Universe. The dim object is a compact galaxy made of blue stars
that existed 'only' 480 million years after the Big Bang; it is tiny
-- over 100 such mini-galaxies would be needed to make up our Milky
Way. It was identified in the Hubble infrared 'ultra-deep field' --
data taken in the late summers of both 2009 and 2010 -- as a faint dot
of starlight. It is visible only at the farthest-infrared wavelengths
observable by Hubble, suggesting that the expansion of the Universe
has reddened its light more than that of any other galaxy previously
identified in the field. Astronomers are surprised to have found only
one; that may indicate that the Universe was changing very rapidly in
early times. Previous searches had found 47 galaxies at somewhat
later times, when the Universe was about 650 million years old. The
Carngie Institution item reported here somehow deduces from those
figures that the rate of star birth increased by about ten times while
the Universe aged by about a third, but the statistics are in any case
more than slightly shaky when they depend upon only one object.
SOLAR SAIL UNFURLS
NASA
The 'NanoSail-D' spacecraft has unfurled a sheet of space-age fabric
650 km above the Earth, becoming the first solar sail in Earth-orbit.
NanoSail-D spent the previous month and a half stuck inside its mother
ship, the Fast, Affordable, Science and Technology SATellite
(FASTSAT). FASTSAT was launched in November with NanoSail-D and five
other experiments onboard. In orbit, a spring was supposed to push
the 30 x 10 x 10-cm probe into an orbit of its own with room to unfurl
a sail. But when the moment arrived, NanoSail-D became stuck in what
was seen as another failure in the long and troubled history of solar
sails. (This one is actually NanoSail-D2; D1 was lost when its
launching rocket failed to reach orbit.) The engineering team on the
ground began to give up hope as weeks went by and NanoSail-D remained
stubbornly and inexplicably onboard, but on January 17, for unknown
reasons, it spontaneously ejected itself. It still had actually to
unfurl its sail. That happened on January 20 and was set off by an
onboard timer: a wire burner cut the piece of fishing line holding the
spacecraft's panels closed and a second wire burner released the
booms. Within seconds they unrolled, spreading a thin polymer sheet
of reflective material into a 10-square-metre sail. Only one
spacecraft has done such a thing before: Japan's IKAROS probe deployed
a solar sail in interplanetary space and used it to fly by Venus in
2010. IKAROS is using the pressure of sunlight as its primary means
of propulsion -- a landmark achievement, which has encouraged JAXA to
plan a follow-up solar-sail mission to Jupiter. NanoSail-D will
remain much closer to home: its mission is to circle the Earth and
investigate the possibility of using solar sails as a tool to de-orbit
old satellites and space junk. The sail's orbit skims the top of our
atmosphere, and the aerodynamic drag will bring it down. Mission
planners expect it to return to Earth, meteor-style, in 70 to 120
days.
SARK BECOMES WORLD'S FIRST DARK-SKY ISLAND
RAS
The Channel Island of Sark has been recognised for the quality of its
night sky by the International Dark-sky Association (IDA), which has
designated it the world's first dark-sky island, the latest in a
select group of dark-sky places around the world. The announcement
was hailed as a great success by astronomers. Sark has no public
street lighting, and there are no paved roads or cars, so it does not
suffer from the effects of light pollution in the same way as towns
and cities do. Many local residents and businesses have altered their
lighting to make them more sky-friendly, ensuring that as little light
as possible spills upwards,
