Podcaster: Morgan Rehnberg

Monthly-News-RoundupTitle: Monthly News Roundup: Pushing Boundaries

Link :
Siding Spring:
New Horizons:
Superluminous galaxy?:

Description: Description: In this episode of the Monthly News Roundup, astronomy pushes the boundaries of exploration both on Earth and in space. A chance encounter yields dividends and new observations deepen a cosmic mystery.

Bio: Morgan Rehnberg is a graduate student in astrophysics and planetary science at the University of Colorado – Boulder. When not studying the rings of Saturn, he develops software to help search for asteroids that might hit the Earth. He blogs and podcasts about astronomy and space science at

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by — no one. We still need sponsors for many days in 2014, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at



You’re listening to the 365 Days of Astronomy podcast for October 30th, 2014. I’m Morgan Rehnberg and this is the Monthly News Roundup. This episode was produced by Cosmic Chatter and recorded October 24th from Boulder, Colorado.


Our top story this month is the close approach of comet Siding Spring to the planet Mars. This comet, also known by the official designation C/2013 A1, came as close as about 140,000 kilometers from the Red Planet on October 19th. That’s only about half the distance between the Earth and the Moon! Siding Spring was first discovered just a year and a half ago, so scientists didn’t have very long to plan observations of this remarkable flyby. Nevertheless, one of the most impressive coordinated campaigns in the history of space exploration has resulted in unprecedented observations of this icy body.

NASA used five spacecraft, Mars Reconnaissance Orbiter, Mars Odyssey, MAVEN, Opportunity, and Curiosity to study Siding Spring. Back at Earth, the Hubble Space Telescope turned its piercing gaze Marsward and a host of ground-based observatories in the Southern Hemisphere also focused in.

So, why all the fuss? Siding Spring was once a member of the most elusive class of solar system object – the Oort cloud, a vast group of objects orbiting hundreds of times farther out than the planets. Unlike the comet currently being studied by the European spacecraft Rosetta, which has orbited within the inner solar system for perhaps millions or billions of years, Siding Spring is what astronomers call a dynamically-new comet. This means that it’s making its very first ever trip in towards us. About a million years ago, a close encounter with another Oort cloud object likely deflected it towards the Sun, a direction it has been traveling in ever since. After passing Mars, it will approach as far in as just outside the Earth’s orbit, before swinging around and returning to the bleak desolation of the outer solar system.

Because this is Siding Spring’s first close approach to the Sun, it has yet to be substantially changed by interactions with our star. This means that it is perhaps our best-ever sample of what these mysterious Oort cloud objects look like. Initial observations show that it’s far smaller than expected. Even though its coma, the cloud of dust and gas surrounding it, is larger than the Earth, the icy nucleus at its center is no bigger than a sports stadium. And, as it basks in the heat of the Sun, it is losing more than 100 kilograms, or 220 pounds, a second. That’s one heck of a diet!

As the comet continues its swing through the solar system, scientists will continue to track it and watch to see what sorts of changes it undergoes. But, this will be our one and only chance to catch a glimpse of Siding Spring. As it moves back beyond the orbit of Jupiter, it will fade from our view and head out to the far reaches of the solar system, not to return for another million years.


While Siding Spring might represent s once-in-a-lifetime opportunity, perhaps October’s most exciting news came from the New Horizons mission. This month they announced that, just in the nick of time, they had found an object for the spacecraft to visit after flying by Pluto next year. And, of course, when it rains, it pours, so they found not one possible destination, but three!

You might recall that New Horizons is hurtling towards a rendezvous with Pluto next year. But, mission controllers never intended for its flyby of this dwarf planet to mark the end of the mission. Instead, having already spent nine years flying out beyond the orbit of Neptune, they mean to see as much as possible. There was only one problem – they couldn’t find anywhere to go.

Out past the farthest planet, even the most reflective objects become faint and difficult to see. Not to mention, space is big. Very big. All this added up to a dearth of known objects nearby to Pluto in the so-called Kuiper belt. In order to plan their trajectory and use New Horizons’ limited fuel effectively, engineers need to know the destination early. So, when the clock ticked down below one year to go this past summer, scientists began to worry. One of our most powerful astronomical instruments, the Hubble Space Telescope was brought in on the search.

We got good news this month when astronomers analyzing Hubble data recovered a trio of small objects along the path of New Horizons. In fact, we could have scarcely hoped for better news – visiting one of these guys will only use up about a third of the spacecraft’s remaining fuel, leaving plenty in reserve. That doesn’t mean, however, that it’ll be a quick trip. New Horizons will need to travel for another three and a half years after passing Pluto to reach this area of the Kuiper belt.

So, what do scientists hope to discover by studying one of these remote objects? The short answer is anything and everything. Up till now, the only Kuiper belt-like object we’ve gotten a close up look at is Neptune’s moon Triton. Next year we’ll add Pluto and its moon Charon to the list, but, for a class of objects that hugely outnumbers the planets, we know almost nothing at all about them. So, even just bringing the total number observed from three to four will be a big deal. Beyond simply that, we will hopefully begin to understand the strange environment of the outer solar system, one in which the Sun is but a faint blip in the sky.


Let’s swing back to Earth now for the groundbreaking of what will soon become the largest telescope on Earth. Work began on Mauna Kea, in Hawaii, this month on the Thirty Meter Telescope, often referred to simply as TMT. It’s the first in a new wave of super-observatories that will spring up over the next decade.

So, what makes telescopes like TMT so super? In a word, size. Today the largest telescope on Earth, Keck, has a mirror which spans ten meters, or about thirty feet. As you might imagine, the Thirty Meter Telescope will have a reflector three times as large. That might seem like a big leap, but it’s probably bigger than you’re even imagining. A three-times broader mirror means it can collect nine times as much light. And, state-of-the-art instruments and technology mean that TMT will be up to 81 times as sensitive as Keck.

Project managers hope to have the telescope up and running by the early 2020s. Once fully operational, astronomers will use TMT to push the boundaries of many research fields. With it, they will be able to gather light from the very first stars in the Universe, study how these stars clumped into galaxies, and where the supermassive black holes found in many galactic cores came from. More precise measurements will also enable a better understanding of the elusive dark matter and mysterious dark energy.

Competition in the arena of enormous telescopes is heating up. By the time TMT is completed, the smaller-yet-still-enormous Giant Magellan Telescope should be complete. And the European Southern Observatory expects its European Extremely Large Telescope, a 39-meter behemoth, to be making its first observations around the same time, as well. But, this is all good news. With the whole Universe to study, we need as many windows into the cosmos as we can possibly get.


Finally this month, the discovery of a fascinating new black hole that challenges our assumptions about how these amazing objects work. When astronomers use x-ray telescopes like NASA’s Chandra Observatory to look out at the Universe through light much shorter in wavelength than what our eyes can see, they often observe bright splotches. Over the last few decades, we’ve deduced that these spots indicate a special kind of binary object. Instead of two normal stars orbiting each other, which occurs frequently in the galaxy, a star is orbiting something far denser – either a neutron star or a black hole.

The intense gravitational pull around objects like black holes lead them to steal matter from the very surface of its companion star. As this gas spirals into the black hole, it gets bunched up, raising its pressure and temperature. As anyone who’s ever seen a blowtorch before knows, the hotter something is, the brighter it glows. The gas falling into black holes is hotter than anything we encounter here on Earth, reaching temperatures of millions or even billions of degrees! This incredible energy is radiated away in the form of x-rays, forming the bright spots seen by astronomers.

But, once in a while, we observe something even brighter still. These so-called ultraluminous x-ray sources have long been a mystery to scientists. That’s because of a law of astrophysics known as the Eddington Limit. It notices that the more and more gas that crowds around a black hole, the brighter and brighter it shines. But light itself exerts a pressure, and as an object becomes brighter it also becomes more forceful. This pushes away any new gas trying to join the party and sets an effective upper limit on the brightness of such objects.

So, then, how can these ultraluminous x-ray sources exist? Astronomers have a couple of ideas. One possibility is that these black holes are simply larger than we think. With more mass comes the ability to pull in more gas and shine more brightly. Another possibility is that these objects are shining like lighthouses – very brightly in one direction and not at all in others. So-called pulsars seem to exhibit this behavior.

Earlier this month, however, astronomers for the first time were able to measure the mass of a black hole at the center of an ultraluminous x-ray binary and they found it was not, in fact, larger than expected. But, it also didn’t display the lighthouse-like characteristics of a pulsar. What could be going on here? We simply don’t know.

This is the exciting part of science. We had a idea about how something in the world works. We tested it and our idea seems to be incomplete. Rather than cause despair, I’m certain that this will energize new researchers to attack the problem, propose new ideas, and design experiments to test them. And one day, hopefully sooner rather than later, we’ll figure out the answer. I can’t wait!


Thanks for listening to this episode of the Monthly News Roundup. For more astronomy news and commentary, visit or follow @cosmic_chatter on Twitter. As always, you can contact us with your comments and corrections at See you in November!


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