Astronomy - June 2015

(Jacob Rumans) #1

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16 ASTRONOMY • JUNE 2015
A suite of spacecraft currently
circle and crawl across the
Red Planet, monitoring every-
thing from its ancient past to
current weather cycles. So it
came as a shock in 2012 when
amateur astronomers using
relatively small earthbound
telescopes started reporting
strange clouds high above
the martian surface.
At least 18 amateur astron-
omers captured the clouds
over the course of 11 Earth
days before they vanished.
A second cycle hit soon after.
Not one of the armada of
martian spacecraft saw the
clouds, but a survey of archi-
val Hubble Space Telescope
images showed similar fea-
tures have been recorded
in the past.
A group of astronomers
used the recent amateur observations to
measure the clouds’ height and came up with
some baffling results. If the scientists’ mea-
surements are correct, the clouds climb more
than 125 miles (200 kilometers), putting them
firmly into the ionosphere and exosphere.
That’s higher than any feature ever seen on
Mars. Stranger still, the clouds morphed over
the course of observing sessions.
The scientists wrote about their find in the
February 26 Nature and said that ice particles
— possibly carbon dioxide or water — and
aurorae might explain the phenomena, but
both of those possibilities would defy the cur-
rent understanding of Mars’ atmosphere. The
plumes rise to twice the height of typical ice
clouds, three times higher than dust storms,
and climb even higher than aurorae. Nothing
has ever been observed on Mars at this alti-
tude before.
Another ill-fitting alternative would be
dust, which would have a tough time circulat-
ing so high and be more likely to do so dur-
ing the day rather than at night — the only
time these plumes were seen.
The astronomers noted that strong
magnetic activity has been seen in the same
region before but added that if these plumes
are tied to aurorae, their brightness would
be some 1,000 times greater than the earthly
version. And solar activity wasn’t high at
the time. — E. B.
Mysterious Mars clouds stump scientists
Astronomers Dan Milisavljevic of the Harvard-
Smithsonian Center for Astrophysics and Rob
Fesen of Dartmouth College used infrared
observations to peek into the hidden heart of
supernova remnant Cassiopeia A. They found
a Swiss-cheesed interior comprising about a
half dozen large bubbles blown by the explod-
ing star 340 years ago. Studying these bubbles
can help astronomers understand the complex
physics of a stellar explosion. They published
their most recent findings in the January 30
issue of the journal Science. For more details
on their work with Cas A, see their story in
Astronomy’s October 2014 issue. — K. H.
CT scan of a
supernova remnant
25 years ago
in Astronomy
In June 1990, Jeff Kanipe
shared new results from
the Cosmic Background
Explorer (COBE), which
had just discovered the
remarkably uniform
temperature of the
microwave background.
COBE’s results were a
Nobel Prize-winning
accomplishment.
10 years ago
in Astronomy
In the June 2005 issue
of Astronomy, Gerry
Bryne delved deep
into the Sun’s frustrat-
ingly unpredictable
activity cycle, high-
lighting new research
that scientists hoped
would allow more
accurate future pre-
dictions. — K. H.
VENUS
IN THE EVENING
DARK MATTER EXTINCTIONS? A biologist tracked the solar system’s past movements through the galactic disk, where
it might meet increased amounts of dark matter, and thinks he’s found a link to comet impacts and geologic activity.
BRILLIANT PLANET. How dazzling is Venus? Even on a bad day, it shines nine times brighter than the night
sky’s brightest star, Sirius. But Venus stands out even more when it blazes against a dark sky, as it will when it
reaches peak altitude in May’s evening sky. This chart plots the positions of Venus during its past four appari-
tions for an observer at 40° north latitude an hour after sunset. Notice that the planet’s peak altitude often
doesn’t coincide with its greatest solar elongation (dates highlighted in white). ASTRONOMY: RICHARD TALCOTT AND ROEN KELLY
MARTIAN METEOROLOGY. NASA’s bevy of instruments missed these
clouds, but watchful amateur astronomers helped researchers calculate the
phenomenon’s inexplicable heights. GRUPO CIENCIAS PLANETARIAS (GCP) – UPV/EHU
RECONSTRUCTING AN EXPLOSION.
Astronomers used infrared observations to determine
the velocity of gas (speed toward the observer is
indicated in darker blue) throughout Cassiopeia A,
revealing the details of a supernova explosion 340
years past. D. MILISAVLJEVIC (CFA)/R. FESEN (DARTMOUTH); BACKGROUND IMAGE:
NASA/ESA/HUBBLE HERITAGE TEAM
From 40° north latitude, Venus peaks at
an altitude of 27° this May. It appeared
some 5° higher in March 2012, its only bet-
ter performance in the past five years.

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