Title: New World Ordered
Podcaster: Daniel Raffaele
Description: Daniel Raffaele talks about exoplanets: the discoveries so far, the potential for new discoveries, and what it is that we are actually looking for. New technologies, such as Infra-Red, allow us to see much smaller planets orbiting closer to their stars, so what does this mean for us on Earth?
Bio: Raffaele was born and raised in Sydney, Australia. He has been a backyard astronomer for many years and by the time this goes to air he will be studying his Masters of Science in Astronomy through Swinburne University of Technology. His interest is the Solar System, particularly planetary science, dwarf planets and exoplanets.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by “Exoplanetology.com – The Art & Science of New Worlds”.
G’Day! From Parramatta, New South Wales – Home of Australia’s first observatory in 1822 – you’re listening to the 365 Days of Astronomy Podcast for Saturday the Fourth of July, 2009 – New World Ordered. My name is Daniel Raffaele. And, on this day in 1997 Pathfinder landed on Mars, in 2005 the Deep Impact collider hit comet Tempel 1 and in 2006 the space shuttle Discovery embarked on mission STS-121 to the International Space Station.
It’s often claimed by environmentalists that we should take care of our planet, because it’s the only one we have. Now, no-one – at least in this day and age – can argue against that. However, it may not be true – at least, not in the future. With the launch of Kepler back in March, our skies are set to become a lot more crowded and we are about to begin to think about starting to possibly answer the question: “Are we alone?”
Of course, it didn’t start with Kepler. We need to go back to 1992 and the discovery of two chthonian planets orbiting the pulsar PSR B1257 +12, followed in 1995 by the discovery of a gas giant orbiting the star 51 Pegasi. It was given the rather unimaginative name of 51 Pegasi b, and I’ll talk more about that shortly, though it is commonly known by the name Bellerophon after the Greek hero who tamed Pegasus. Only two other extra-solar planets have names: Osiris (HD 209458 b) and Methuselah (PSR B1620-26 b) – although the latter is unofficial.
So, why have only three extra-solar planets discovered thus far been assigned names? Really, it’s just the sheer number. More than three-hundred – and that’s pre-Kepler. Add to that the ever emerging dwarf planets in the Kuiper Belt and the ever increasing number of moons orbiting Jupiter and Saturn and we have ourselves a problem. There’s a real possibility that sometime in the future the number of planets will exceed the number of words that can be used as names. This issue was quickly encountered when the stars were catalogued. Only the brightest, most notable stars were named. So it may be that only the most exceptional extra-solar planets will get names.
Bellerophon was the first extra-solar planet to be verified. Osiris has signs of water vapour and Methuselah’s system had a really interesting evolution which could fill a whole show all by itself, so I won’t go into detail. Perhaps the next name is reserved for the first truly Earth-like planet we find.
So, what are we looking for? We really only need to fill three criteria: mass, location and chemistry. The planet can’t be too small, otherwise it won’t produce enough gravity to hold onto an atmosphere – let alone us. It can’t be too big, otherwise you have a hot super-Earth with a heavy, toxic atmosphere and a crust in danger of collapsing in on itself, or a cold super-Earth with a heavy, frigid atmosphere and a crust that has collapsed in on itself. Ideally, we want something no less than roughly three-quarters the mass of Earth – and even that’s pushing it – up to no more than around twice the mass of Earth. Again – pushing it.
As for location, we look for what’s called the Habitable Zone. This is the distance from a star where water can exist as liquid. In the Solar System, Earth is nicely situated right in the middle of our Sun’s Habitable Zone. Increase the mass and luminosity of the star and you move the Habitable Zone further out. Decrease the mass and luminosity of the star and you move the Habitable Zone further in. For binaries, the maths gets a bit scary. We can rule out pulsars and variable stars entirely.
I now want to take a moment to talk about something a little closer to home. Venus and Mars, both of which just squeeze into the Sun’s Habitable Zone. At about 0.85 Earth mass Venus is often called “Earth’s Twin.” However, the similarities end there. Venus is cursed with a runaway greenhouse effect brought about by it’s extremely dense carbon dioxide based atmosphere. Not a nice place to visit and you certainly wouldn’t want to live there. Mars, on the other hand, has a thin, frigid carbon dioxide based atmosphere – due to it’s low gravity – no ozone layer and neither have a magnetic field to speak of. What we need is a nitrogen based atmosphere with pressure of around one-hundred kilopascals to be comfortable, along with adequate protection from ultra-violet and solar radiation.
As I’ve discussed, there have been numerous attempts to find such a planet using a wide range of techniques and so far turning up over three-hundred results – none of which fit the bill for a new Earth. The methods used range from pulsar timing which gave us our first results back in 1992, to radial velocity, or Doppler spectroscopy, as is the case with Bellerophon. In this decade, techniques for detection have included gravitational lensing and direct imaging using infrared. Most notably, however, was the 2008 discovery of Fomalhaut b using good old visible light. The Keck Observatory uses interferometry, as will the upcoming Space Interferometry Mission and part of the much anticipated Terrestrial Planet Finder, which will also use optical detection.
Kepler uses the transit method. This is the fairly straight forward technique of watching a star for a long time to see if anything passes in front of it. Searching an area between Cygnus and Lyra, it will continually monitor more than one-hundred-thousand main sequence stars over the next three-and-a-half to six years.
What Kepler finds in that time entirely depends on what’s there to be found. Now, I know that’s an obvious statement, but it’s mass that matters here. If most planets in the target field of view are roughly the same mass as Earth and none are any bigger, we can expect to here of about fifty. Allow for an upper limit of 1.3 Earths and the number balloons out to one-hundred-and-eighty-five. If we’re particularly generous with our upper limit and allow for planets up to 2.2 Earths, it’s a staggering six-hundred-and-forty. We can also expect roughly one in eight stars with systems to have two or more companions.
Due for launch sometime between 2010 and 2015, the SIM Lite Astrometric Observatory expects to find around forty-two stars with with planets the mass of Earth and around sixty-nine stars with planets that are twice as massive as Earth.
Hopefully before 2020, the pinnacle of the search will see the launch of the Terrestrial Planet Finder. Using a combination of a visible light coronagraph and a formation flying infrared interferometry array, this mission will allow us to see our galaxy like w’eve never seen it before and will make the Sloan Digital Survey look like a backyard astronomer’s happy snaps. There’s simply no telling, at this stage at least, how many planets it will find.
So, that’s the mass requirement satisfied. Now all that remains to be seen is how many of the new discoveries fulfill the equally important criteria of location and atmospheric chemistry. Odds are that at least a few will. It is highly unlikely, given the number of planets expected to be found, that the whole effort would be for naught. In fact, using a conservative estimate of only one percent of Earth-like planets being in the Habitable Zone, limiting ourselves to planets roughly the same mass as Earth and assuming the atmospheric conditions are conducive to life, we can expect to find at least three planets (or, possibly, even a moon) suitable for habitation in our neighbourhood by 2025.
Which brings us to the issue of getting there. Well, obviously we can’t get there. There is just too far away. It’s not necessarily the number that matters here, it’s the unit of measurement that follows the number that’s the deal killer. Light Years, or, more commonly, Parsecs. So, it seems that no human who walks the Earth today will walk the New Earth tomorrow. It will be left to our descendants, who will see us as their ancients, to bridge the gulf of inter-stellar space and maybe, just maybe, humanity will survive long after our planet has been swallowed by a dying star.
For show notes and links to a wealth of extra-solar planet resources, visit: july4shownotes.blogspot.com. Thanks for listening and I hope you enjoy the remaining one-hundred-and-eighty days of astronomy. Goodbye.
End of podcast:
365 Days of Astronomy
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