BellaOnline Forums Education Astronomy Top Ten Astronomy Stories 2015 *new*

Some called 2015 "The Year of the Dwarf Planet" because space missions visited both Pluto and Ceres. Elsewhere Philae briefly awoke on a comet. Water was found on Mars, and so was Beagle 2. But how did astronomers predict a supernova, and what is the most distant known object in the Solar System?

Top Ten Astronomy Stories 2015

My favorite picture of Pluto from New Horizons is the false color one that emphasizes the heart shape and brings up the contrasts in Pluto's terrain. Fascinating.

Pluto's large moon Charon certainly had planetary scientists excited. They scarcely dared hope that it would be this interesting. Its surface is varied and an enormous system of fractures and canyons circles it.

Here are three articles about Pluto that might interest you:
Pluto – Gateway to the Kuiper Belt
Pluto Is a Dwarf Planet
Eris and Pluto – They're not Twins

More to come when the New Horizons data makes it home!

Ceres was the first asteroid/dwarf planet to be discovered. This was on January 1, 1801. Asteroids are hard to spot, so it made sense that the biggest one was found first. As telescopes got better, the number of discoveries increased.

But never mind the telescopes, nothing better than having a probe orbiting Ceres. Scientists and the public were intrigued by the mysterious bright spots Dawn was showing in photographs. What did people think they were? - lots of people made their guesses. Who was right?

I'd say those that went for "salt deposits" were closest. It's not table salt, but a mineral salt, that's responsible. It's the sort of mineral salt left behind when ice sublimes (goes from solid to gas without melting). The fact that these deposits are found all around Ceres strongly suggests a layer of briny ice under the surface.

There was much excitement when the Philae lander contacted Rosetta and the message was relayed home. The Rosetta people never did work out exactly where Philae was, but narrowed it down to a small area of Comet C-G .

Being closer to the Sun gave Philae a better chance of recharging its solar batteries and communicate. However closer to the Sun also made the comet more active and therefore more difficult to achieve contact with Philae.

After Comet C-G passed perihelion (its nearest approach to the Sun), Rosetta's mission was extended. This means that scientists will now be able to see the changes as it heads away from the Sun and back to a cooler part of the Solar System.

Here is the most recent image release - this was taken on January 6, 2016 .

After all the years of evidence that water had been on Mars in the distant past, NASA found some in the present. The central mountains of Hale Crater are one of four locations with flowing saltwater rivers. They're seasonal and extend from bedrock cliffs. They're most active mid-summer.

Image credit: NASA/JPL-Caltech/University of Arizona.

The Mercury Surface, Space Environment, Geochemistry and Ranging (Messenger) mission ended on the last day of April. Its original 1 year stretched to 4 years. When the propellant ran out and the Sun's gravity was ready to drag the craft down, controllers got some extra time by using some helium that was originally carried to pressurize the fuel.

They did a good job predicting the date and time for Messenger's plunge to the planet. A farewell was tweeted to its followers:

Here was Messinger's last image of Mercury's surface. A job well done.

Dear Mona,

Wow! How incredible is this?

I hope they never stop exploring! I'm always curious about what's up there!

Mary Caliendo
Tea Editor

Last year a 12-year-old mystery was solved. On Christmas Day 2003, Beagle 2 - a little UK lander - was due to land on Mars. It had been inserted into orbit by ESA's Mars Express, but Beagle never phoned home. Nor was it, or its debris, found. In January of last year it was announced that the wreckage of Beagle 2 had been found in Mars Reconnaissance Orbiter images. It landed about where it should have, but not all of the solar panels unfolded, so the antenna couldn't be raised.

For over twelve years Eris - Dwarf Planet and its moon were the most distant known bodies in the Solar System (except for comets). But late last year - it was announced in November - V774104 was discovered by Scott Sheppard, Chad Trujillo and David Tholin.

V774104 is at 103 AU, which means it's over a hundred times farther from the Sun than Earth is. In earthly distance terms, it's 15.4 billion km / 9.6 billion miles. Astronomers think it's icy object 500-1000 km across, and that it could be part of the Oort Cloud, but they don't currently know anything about it's orbit. That will take at least a year of observation.

The Refsdal Supernova keeps reappearing. The Hubble image shows the past, present and predicted future of the supernova's appearances. The star only blew up once, but the event is being gravitationally lensed by a massive galaxy cluster in front of it. Distant events can not only be magnified by such a lens, but multiplied. The light from the supernova is bent around the cluster so that it reaches us on different paths. They don't all take the same amount of time to get here, so we see more than one image.

The top circle represents 1995, though the supernova wasn't actually observed then. The lowest circle shows the galaxy which lensed the Refsdal Supernova to produce four images — a discovery made in late 2014. The middle circle shows the predicted position of the reappearing supernova. It did reappear there last year.

G is for Gravitational Lens will tell you more about this lensing effect.

Image Credit: NASA, ESA, S. Rodney (John Hopkins University, USA) and the FrontierSN team; T. Treu (University of California Los Angeles, USA), P. Kelly (University of California Berkeley, USA) and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; and Z. Levay (STScI)

The Refsdal Supernova was named for Norwegian astrophysicist Sjur Refsdal (1935-2009). He did pioneering theoretical work on gravitational lenses in the 1960s, including their effects and possible applications. It had to be theoretical, because the first gravitational lens wasn't discovered until 1979.

In the center of the Hubble image of QSO 0957+561 is what seems to be two very similar quasars, and called the Twin Quasar. Then astronomers realised that these twins are a little too identical - they're close together, at the same distance from us, and have surprisingly similar properties. They're actually two images of the same object which has been gravitationally lensed.

Not many people saw the total solar eclipse in March 2015. The path of totality went over the Faroe Islands and the Svalbard Archipelago. Neither place is densely populated nor usually high on the March tourist agenda. The weather was against observers in the Faroes, but there were still some who saw totality. Cold in Svalbard, but many got a clear sky.

The Astronomy Photographer of the Year 2015 winning photograph was taken by Luc Jamet in Svalbard. Svalbard is about halfway between the northernmost part of Norway and the North Pole.

In the picture, all we see is the Sun's bright corona. A desolate snowy landscape is dark beneath the eclipsed Sun. Yet in the sky you can see where the Moon's shadow ends. Venus is the bright spot in the upper left. One of the judges described it as “otherworldly”.

I was in northern Norway at the time and saw a substantial partial eclipse in a partly cloudy sky. Not as good as a total eclipse, of course, but still a lovely sight.