Podcaster: Morgan Rehnberg

Title:  Monthly News Roundup – Water, Water, Everywhere

Link :

Dark matter:
Water worlds:
Saturn rain:
Mars conjunction:
Kepler’s Supernova:
Exoplanet names:

Description: It’s a wet month in the universe: new ocean worlds are discovered and Saturn’s rings are raining onto the planet.  A hint of dark matter is found at the ISS and new details emerge about Kepler’s Supernova.  Scientists and rovers alike take a spring break as Mars enters conjunction.

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 2013, 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 April 28th, 2013.  I’m Morgan Rehnberg and this is the Monthly News Roundup.  This episode was produced by Cosmic Chatter and recorded April 24th from Boulder, Colorado.


Let’s start this month with a trip to the International Space Station.  Orbiting more than four hundred kilometers above the surface of the Earth, the ISS is our only continuously-manned outpost in space.  With a cost exceeding 150 billion dollars, it’s also the most expensive project in human history.  Given this, there has always been enormous pressure to generate scientific results from this orbiting laboratory.  While many experiments have been conducted, particularly in the biology of living in space, there’s never been a headline-grabbing result.  That may have changed this month with the possible discovery of signs of dark matter.

Dark matter is one of the great unsolved mysteries of modern physics.  Although scientists have never observed it, we think that there is about five times more dark matter in the Universe than ordinary matter.  Dark matter is so difficult to detect because it doesn’t interact with light – our principal tool for studying the cosmos.  Instead, we can only infer its existence indirectly.  For example, galaxies seem to have much more mass than is accounted for in all the matter we can see.  This causes the galaxy to rotate more quickly than it otherwise would.

What’s really needed is a so-called “smoking gun experiment” – an experiment that reveals results that cannot be predicted by our existing understanding of physics.  This latest project goes a long way in that direction.  Called the Alpha Magnetic Spectrometer, this instrument detects a rare particle known as a positron.  Positrons are a kind of antimatter, in this case, the anti-electron.  It has all the same properties as the electron, but instead of a negative charge, it carries a positive one.

It’s predicted than when particles of dark matter collide, they release a shower of positrons, which are eventually collected and measured by the Alpha Magnetic Spectrometer.  Since its launch in 2011, the experiment has detected more than 400,000 of these events.  The only problem is, another astronomical phenomenon, the pulsar, can produce positrons which look similar to those from dark matter collisions.  For the instrument to be able to tell these events apart, it needs more than two years of data.

Fortunately, the Alpha Magnetic Spectrometer will continue to operate until the retirement of the International Space Station, which is at least seven years away.  By then, we’ll hopefully have our first solid evidence that the mysterious dark matter actually exists.


From an Earth-orbiting space station, let’s turn to some Earth-like planets.  Scientists with the Kepler mission announced this month the discovery of a trio of worlds which could support life.  The three planets are so-called super-Earths, because they’re about one and a half times the size of our world.  Known as Kepler 62e, Kepler 62f, and Kepler 69c, these planets all orbit stars which are less than a quarter as bright as the Sun.  They’re in the habitable zone because they orbit closer to their stars than we do to the Sun, allowing them to receive additional heat.

What might these alien worlds look like?  Because they’re so small and far away, we can only speculate.  A model released in conjunction with this announcement, however, suggests that at least two might be covered entirely by water.  Determinations like this are usually made by examining a planet’s temperature and density.  Water is less dense than rock, so if a planet seems fluffier than normal, it probably has a substantial portion of water.  If that planet is warm, like these, this water is probably liquid.  If the temperatures are too low, it’s likely covered in ice.

Water worlds are especially exciting to astrobiologists, because many scientists believe that life here on the Earth began in the oceans.  The oceans act as a giant mixing bowl, stirring together the various organic molecules which form all life on Earth.  Over billions of years, these molecules bump together until they happen to form the earliest cells.

These cells could eventually form more complex life, but could a technological civilization like ours ever exist on a water world?  It seems doubtful.  The foundation of nearly all our technology is fire.  It heats our homes, cooks our food, and powers our machinery.  A planet covered in ocean hardly seems hospitable to fire.

Regardless of whether these planets actually support life, it’s thrilling that we’re finding more and more of them that could.  With every discovery, the universe seems a little less sterile and a little more friendly.


Ever think that the Earth was the only planet in our solar system to have rain?  Think again – scientists have found evidence of rain on Venus, Mars, and Titan – and now you can add Saturn to this list.  Unlike all these other worlds, however, Saturn’s rain has a unique source.  Rather than falling out of atmospheric clouds, rain on Saturn seems to come from its beautiful rings.

The rings are composed of nearly perfectly pure water ice and now it seems that some of that ice escapes and falls onto the planet itself.  How does this work?  Astronomers aren’t really sure.  Somehow, small chips of ice are knocked off the larger chunks which make up the ring, perhaps through collisions.  But in the absence of gravity, how do these chips fall onto the planet?  The answer seems to lie in magnetic fields.  If these fragments have an electric charge, they get caught up by Saturn’s magnetic field and dragged along through space.  Eventually this field must reconnect with the planet, and the ice particles follow along, where they rain down on the gaseous upper layers of Saturn.

If this explanation proves correct, it could open the door for additional magnetic effects.  Saturn’s magnetic field is relatively weak, about five perfect the strength of Jupiter’s and a little weaker than the Earth’s.  Because of this, most structure in the rings has been attributed to the gravitational effects of the planet’s many moons.  Maybe, however, some properties of the rings are affected by the magnetic field.  With the Cassini spacecraft expected to orbit Saturn for another four years, we might not be that far from finding out.


While it was raining on Saturn, it was spring break on Mars.  Every two years, Mars and the Sun reach what’s called conjunction. This means that, as seen from Earth, they’re as close together in the sky as they ever get.  The Sun is a lot bigger than Mars, so it actually blocks it from our view for about a month.  While this is sad news for skygazers, it’s also a bump in the road for Mars exploration.

We currently have five spacecraft at Mars.  Three, Mars Reconnaissance Orbiter, Mars Express, and Mars Odyssey, are in orbit.  Curiosity and its older sibling Opportunity are on the surface.  All of them are in daily contact with engineers and scientists here on Earth.  These communications are carried through the Deep Space Network, which uses a series of giant radio dishes to transmit and receive information from all over the solar system.  When the Sun blocks Mars, however, it cuts the red planet off from this network.  This means that for nearly all of April, spacecraft at Mars were out of contact with Earth.

If you’re a satellite in orbit, you’re pretty safe, and all three Mars orbiters have been carrying out pre-programmed tasks all month.  On the ground, things are a bit more tricky. Although the rovers do have the capability to steer themselves around obstacles, if they were to get stuck they’d have no way to call for help.  Instead, they’ve spent the month performing stationary experiments.  Curiosity has spent her time measuring the water content of the nearby soil, while Opportunity has made atmospheric dust measurements and studied a rock.

When Mars emerges from the Sun’s shadow at the beginning of May, all this collected data will be returned to Earth for study. Then it will be time to get back to work, and not just for the spacecraft.  Many engineers and scientists also used this downtime to schedule their own, much-needed vacations.


Supernovae are relatively common in the galaxy.  On average, a star explodes somewhere in the Milky Way every fifty years.  But it’s far less common for one of these massive explosions to be visible to the naked eye.  It’s been more than four hundred years, in fact, since that last occurred.  Recorded by the famous astronomer Johannes Kepler, supernova 1604 is now better known as Kepler’s Supernova.

This blast was a type 1a supernova, which means that it marked the destruction of an ancient white dwarf star.  Kepler’s Supernova is the most easily-observed type 1a supernova, so it’s a valuable tool for astronomers.

What was the star like before it exploded?  Physical models can provide some clues, but to get a fuller picture we need to study the aftermath of the explosion itself.  A new study has done just that.  Using data collected from the Japanese Suzaku x-ray telescope in 2009 and 2011, a group of researchers have reconstructed the composition of this white dwarf.

They detected small amounts of elements like chromium, nickel, and manganese and a larger amount of iron.  By comparing these measurements to observations of the Sun, they determined that this star must have had about three times the amount of metals contained in ours.  This is curious because older stars typically have fewer metals than recent ones, not more.

With a distance of only about twenty thousand lightyears, the star that led to Kepler’s Supernova was born in our cosmic neighborhood.  This means that as we continue to study it, we may also learn more about the history of our own Sun.


Do you have astronomical favorites?  Maybe your favorite planet is Neptune, your favorite moon Hyperion, your favorite rover Spirit.  But do you have a favorite exoplanet? If so, chances are it has a name like HD 38529 Ab.  Plenty bland, huh?  To try and make these names a bit friendlier, a number of groups have sprung up offering to sell naming rights to recently discovered planets.  Astronomy’s governing body, however, has said “no way.”

Most things in astronomy exist in catalogs.  With as many as 400 billion stars in our galaxy alone, it’d be impossible to creatively name them all.   Let’s take a look at planet HD 38529 Ab.  What does this name mean?  HD means that the star is located in the Henry Draper star catalog, a catalog of the 225,000 brightest stars as seen from Earth.  38529 is the entry in the catalog.  “A” means that this star is a multiple star system and this is the brightest of the stars. “b” means that this is the first planet discovered in the star system, because the star itself is called “Aa.”

So there’s lots of information here, but it’s not very user friendly.  That’s okay with astronomy’s governing body, the International Astronomical Union.  The IAU is charged with standardizing the notation and terminology used by astronomers worldwide.  Best known for demoting Pluto from planethood, they oversee the assignment of names and numbers to newly discovered objects.  They mostly want to keep people from getting ripped off by buying planet names.  Since scientists will continue to use the IAU-approved names, the buyer really isn’t getting anything for their money.

Although it’s impossible to buy the name for any astronomical object, there is one class of objects which can be named.  Anyone who discovers a new asteroid has a certain timeframe to name it as they choose.  So, if you want your own name on the Earth’s killer asteroid, you’d better start making friends!


Thanks for listening to this episode of the 365 Days of Astronomy Podcast.  For more astronomy news and commentary, visit or follow cosmic_chatter on Twitter.  You can send comments and corrections to  See you in May


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365 Days of Astronomy
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