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FRIENDS OF THE PLANETARIUM NEWSLETTER – SEPTEMBER 2014
The European Space Agency's Rosetta spacecraft finally arrived at Comet 67P/Churyumov-Gerasimenko a
month ago, after a 10-year cruise through interplanetary space. In an ideal world, Comet C-G would have been a
nice smooth ball of dust and ice with a big X marking the safest and most scientifically interesting landing site for
the craft's Philae lander. Had that been the case, says Rosetta mission manager Fred Janssen, his team would
have put the odds of a successful landing at 70 or 75 percent. However, nature has thrown the project a few
curves. Not only is the comet's nucleus complicated, an
irregular, double-lobed structure 4 km long, but it's also
much rougher and craggier than expected. The recently
taken image at left shows how irregularly shaped the comet
really is. This photo was taken from a distance of about 30
km. Add to that the comet's ahead-of-schedule activity (it's
already giving off jets of gas despite being 3.4 astronomical
units from the Sun), and all bets are off. At an ESA press
briefing Janssen declined to offer a revised risk assessment.
"No site meets all the engineering criteria," he allowed. That
said, Philae has to set down someplace, and the team has
winnowed down an initial set of 10 candidate sites to
primary and backup locations. The best location, designated
Site J, is on the comet's smaller lobe (think of it as the
"head"); the backup, Site C, is on the larger "body."
Engineers opted to stay clear of the smooth-textured "neck"
between them, because from there it would be difficult for Philae to remain in constant radio contact with the
main spacecraft as it orbits the nucleus. The smaller-lobe site won out in part because cameras have already
identified two small pits near it that are sources of outgassing. Each of Philae's 10 instruments will be able to
operate at least once to its full
capability. Assuming no "gotchas"
emerge, the spacecraft will release
Philae on November 11th for its 7hour-long "fall" to the comet's surface.
Once it makes contact at roughly one
meter per second), the washingmachine-size, 100-kg lander will
anchor itself using a mechanical
harpoon, then quickly take a 360
degree panorama and measure the
pressure of cometary gas surrounding
it. The photo above right shows details of the chosen landing site. It still looks quite dodgy but we all wish ESA
great success.
A total eclipse of the moon takes place on October 8. All phases of the eclipse are visible from New Zealand.
Totality lasts for almost an hour from 11:25 pm to 12:24 pm. The moon starts entering the Earth's umbral
shadow about 10:15 pm and finally leaves it at 1.35 am. Uranus is at opposition on October 8th, the planet will
then be 2844 million km, 19 AU, from the Earth. Consequently the planet will be in the sky all night. It is
currently in Pisces. A few hours after Uranus is at opposition the Earth's moon is in total eclipse. Uranus, at
magnitude 5.7 will be 2 degrees above the moon as seen from NZ. A similar magnitude star will be 1.3 degrees to
the left of Uranus; otherwise there is no object likely to be confused with Uranus in binoculars above the moon.
NASA's Pluto-bound New Horizons spacecraft has traversed the orbit of Neptune. This is its last major crossing
en route to becoming the first probe to make a close encounter with distant Pluto on July 14, 2015.
The sophisticated piano-sized spacecraft, which launched in January 2006, reached Neptune's orbit, nearly 4.4
billion kilometers from Earth, in a record eight years and eight months. New Horizons' milestone matched
precisely the 25th anniversary of the historic encounter of NASA's Voyager 2 spacecraft with Neptune on Aug.
25, 1989. "It's a cosmic coincidence that connects one of NASA's iconic past outer solar system explorers, with
our next outer solar system explorer," said Jim Green, director of NASA's Planetary Science Division. "Exactly 25
years ago at Neptune, Voyager 2 delivered our 'first' look at an unexplored planet. Now it will be New Horizons'
turn to reveal the unexplored Pluto and its moons in stunning detail next summer on its way into the vast outer
reaches of the solar system." Several senior members of the New Horizons science team were young members of
Voyager's science team in 1989. Many remember how Voyager 2's approach images of Neptune and its planetsized moon Triton fueled anticipation of the discoveries to come. They share a similar, growing excitement as
New Horizons begins its approach to Pluto. Similar to Voyager 1 and 2's historic observations, New Horizons
also is on a path toward potential discoveries in the Kuiper Belt, which is a disc-shaped region of icy objects past
the orbit of Neptune, and other unexplored realms of the outer solar system and beyond.
Once every 50 years, more or less, a massive star explodes somewhere in the Milky Way. The resulting blast is
terrifyingly powerful, pumping out more energy in a split second than the sun emits in a million years. At its
peak, a supernova can outshine the entire Milky Way. It seems obvious that you wouldn't want a supernova
exploding near Earth. Yet there is growing evidence that one did, actually, more than one. About 10 million
years ago, a nearby cluster of supernovas went off like popcorn. We know because the explosions blew an
enormous bubble in the interstellar medium, and we're
inside it. Astronomers call it "the Local Bubble." It is peanutshaped, about 300 light years long, and filled with almost
nothing. Gas inside the bubble is very thin (0.001 atoms per
cubic centimeter) and very hot (roughly a million degrees),
a sharp departure from ordinary interstellar material. The
Local Bubble was discovered gradually in the 1970s and
1980s. Optical and radio astronomers looked carefully for
interstellar gas in our part of the galaxy, but couldn't find
much in Earth's neighborhood. Meanwhile, x-ray
astronomers were getting their first look at the sky using
sounding rockets and orbiting satellites, which revealed a
million-degree x-ray glow coming from all directions. It all
added up to Earth being inside a bubble of hot gas blown by
exploding stars. Obviously, those supernovas were not close
enough to exterminate life on Earth, but they were close
enough to wrap our solar system in a bubble of hot gas that
persists millions of years later.
Do you know where you live? You probably know your street address and the name of your town, region, and
country. But what about your cosmic address, your location among the stars? Thanks to efforts by some
astronomers in Hawaii, you can now tell people you live in Laniakea. Scientists have known for decades that our
solar system rests on an outer arm of the Milky Way galaxy. In turn, galaxies are not sprinkled randomly
throughout the cosmos; they cluster into groups, which themselves are part of larger groups. What has been
known is our Milky Way is part of the Local Group, a collection of galaxies some 10 million light-years across.
Based on work by Gerard de Vaucouleurs in the 1950s, astronomers have thought of our galaxy as being on the
edge of the so-called Local Supercluster, a structure about 100 million light-years wide that’s centered on the
Virgo Cluster of galaxies. Now, a team of scientists led by University of Hawaii astronomer R. Brent Tully have
mapped the boundaries of a massive "supercluster" of galaxies stretching 500 million light-years through space.
They named the supercluster "Laniakea," a Hawaiian word meaning "immense heaven." As a side benefit to
identifying a new structure in the universe, the largest yet known, the team's efforts shed light on what's called
the Great Attractor. Scientists have known of a perturbation in the general cosmic expansion, a "pull" towards a
particular part of the sky, for 40 years, and for nearly 30 have known in what direction it lies. Its nature, though,
has remained a mystery. The mapping of Laniakea enables astronomers to conceptualize the Great Attractor as
the basin of a gravitational "valley", the end point of the supercluster's watershed.