Shasta Astronomy Club
Newsletter
NASA’s Curiosity Rover Spots Purple Rocks on
Mars
composition of these different rock layers can help scientists
learn more about Mars’ past.
By Samantha Mathewson
The images have a white-balanced color adjustment that
resembles how rocks and sand would appear under daytime
lighting conditions on Earth. This helps geologists who study
the rocks recognize color patterns that they are familiar with on
Earth, NASA officials said in the statement.
Mars may appear red when viewed from Earth, but NASA’s
Curiosity rover has captured an up-close photo of the planet’s
mountainous landscape, with purple-colored rocks littered
across the foreground.
This remarkable new photo was captured near the base of
Mars’ Mount Sharp. The image’s three frames were taken by
Curiosity’s Mast Camera (Mastcam)on Nov. 10.
“Variations in color of the rocks hint at the diversity of their
composition on lower Mount Sharp. The purple tone of the
foreground rocks has been seen in other rocks where Curiosity’s
Chemical and Mineralogy (CheMin) instrument has detected
hematite,” or a type of iron-oxide mineral, NASA officials
said in a statement. “Winds and windblown sand in this part
of Curiosity’s traverse and in this season tend to keep rocks
relatively free of dust, which otherwise can cloak rocks’ color.”
Mount Sharp rises 3 miles (5 kilometers) from the center of
Mars’ 96-mile-wide (154 km) Gale Crater. After arriving at the
crater in 2012, Curiosity found evidence that suggested that the
area could have supported microbial life in the ancient past.
In addition to the purple rocks in the foreground, the images
from Curiosity capture higher layers of Mount Sharp. The rover
will continue to traverse these slopes throughout the rest of its
mission.
This uphill trek began in October at the orange-colored rocks
of the Murray formation, near the base of Mount Sharp. Next
the rover will climb upward to the Hematite Unit, followed
by the Clay Unit and the rounded hills of the Sulfate Unit —
which is Curiosity’s highest planned destination. Studying the
The ‘brightest supernova’ might not have been a
supernova at all
A team of researchers say the bright light could have been
caused by a black hole
By Nicole Kiefert New observations from several observatories show that what was
thought to be the brightest supernova ever might have been an
optical illusion of sorts.
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ASASSN-15lh was first detected by the All Sky Automated
Survey for Supernova (ASASSN) and was declared a
superluminous supernova. It was 20 times brighter than the total
light output of the entire Milky Way, giving it the title of brightest
supernova.
However, a team of scientists led by Giorgos Leloudas at the
Weizmann Institute of Science and the Dark Cosmology Centre
has proposed an alternative explanation for ASASSN-15lh.
Due to reserach from observatories, including ESO’s Paranal
Observatory, The New Technology Telescope at ESO’s La Silla
Observatory, and the NASA/ESA Hubble Space Telescope, the
team of astronomers believe that the bright light didn’t come
from ASASSN-15lh, but instead from a rapidly spinning black
hole that was destroying a star that was too close.
“We observed the source for 10 months following the event and
have concluded that the explanation is unlikely to lie with an
extraordinary bright supernova,” Leloudas said in a press release.
“Our results indicate that the event was probably caused by a
rapidly spinning supermassive black hole as it destroyed a lowmass star.”
What they believe happened was that the Sun-like star had gotten
too close to a supermassive black hole and the gravitational
forces stretched the star vertically and compressed it horizontally
until it was destroyed. Then the colliding debris and the heat
generated from the destruction caused the bright burst of light.
“There were several independent aspects to the observations
that suggest that this event was indeed a tidal disruption and
not a superluminous supernova,” said Morgan Fraser from the
University of Cambridge, UK, and coauthor of the study.
The team states that this is a rare event and can only occur with a
very specific type of black hole.
Astronomers examined weather on a scorching hot
exoplanet
This is the first observation of planetary weather outside our
solar system
By John Wenz The weather on sunny HAT-P-7b isn’t so great right now. It’s
cloudy and 3,500 degrees Fahrenheit (1,927 degrees Celsius.)
But that we know this at all is rather revolutionary. That’s
because we’ve only had the slightest whiff of planetary weather
— and this is the first time we’ve directly observed it outside the
solar system. The research was published today in Nature.
The planet is larger than Jupiter, and orbits its home star in a little
more than two days. That places it as a hot Jupiter, a gas giant so
close to its star that it orbits in Earth days rather than a period of
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Shasta Astronomy Club
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months or years. The interaction between the massive planets and
their home stars makes them some of the easiest to detect.
Ancient Astronomers Tell Us Earth’s Days Have
Lengthened
While HAT-P-7b was initially detected by the HATNet program
at the Harvard-Smithsonian Center for Astrophysics, much of
the follow-up observations of the planet came from the Kepler
telescope.
A day on Earth is longer than it used to be. The increase is tiny.
Over the span of a hundred years the Earth’s day will increase
by only a few milliseconds. It’s only been in the past few
decades that we’ve been able to measure Earth with enough
precision to see this effect directly. Using atomic clocks and ultraprecise measurements of distant quasars, we can measure the
length of a day to within nanoseconds. Our measurements are so
precise that we can observe various fluctuations in the length of
a day due to things like earthquakes. Those fluctuations make it
a challenge to answer another question. How has Earth’s rotation
changed over longer periods of time?
Initial Kepler observations from the first four year campaign
showed wild variability in the dimming of the parent star,
HAT-P-7. Based on this data, a team led by David Armstrong
at the University of Warwick were able to assemble a picture
of winds whipping the intense heat of its parent star, which is
larger than the Sun, to the night side of the planet distributing that
heat globally instead of allowing for a hot “day” side and a cool
“night” side.
The specific “smoking gun” was changes in brightness, indicating
the influence of planetary-scale winds that speed up and slow
down due to weather-like phenomena.
Follow-ups with the James Webb Space Telescope could give
unprecedented glimpses into planetary weather — and based on
what we know so far, HAT-P-7b could be an excellent candidate
for follow-up observations.
Part of the reason Earth’s days are getting longer is due to the
gravitational pull of the Moon on our oceans. The tides slosh
against the Earth, gradually slowing its rotation. Over millions of
years this means Earth’s day was hour shorter than it is now, thus
there were more days in a year than today. We see this effect in
the geological record, which tells us an Earth day was about 22
hours long 620 million years ago. Trying to measure the length
of a day between the recent and geological era, however, is
difficult. Hundreds of years ago clocks weren’t accurate enough
to measure this variation, and the length of a day was fixed to
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Shasta Astronomy Club
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its rotation, making any such comparison impossible. But recent
work has found a way to study Earth’s changing days.
tend to shorten Earth’s days a bit. The combination of these two
effects give us the historical rate we see.
Although our ancestors of centuries past didn’t have accurate
clocks, they were good astronomers. They observed and documented astronomical events such as the occultation of bright
stars by the Moon, as well as solar eclipses. The occurrence of
these events depends critically on when and where you are. If, for
example, an astronomer in one city sees the Moon pass in front
of a star one night, an astronomer in a nearby city will only see
the Moon pass close to the star. By comparing the observations
of these astronomical events with the actual time of their event
as calculated from the orbital motions of the Earth and Moon, we
know exactly when and where they occurred. Fitting a history of
observations together, we can get an average rate for the increase
of a day. That turns out to be about 1.8 milliseconds per century.
There are two things that are interesting about this result. The
first is that it’s pretty amazing to be able to determine this rate
from historical documents. The observations span more than two
and a half millennia, and are written in various languages and
locations. Gathering them all together and verifying them is an
amazing effort. The other is that this rate is actually less than the
rate theorized from the tidal effects of our Moon (about 2.3 ms/
century). This is likely due to changes in Earth’s overall shape.
We know, for example, that the melting of ice since the last ice
age (about 10,000 years ago) has released pressure at the Earth’s
poles, allowing it to return to a more spherical shape. This would
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