Alien planets–or exoplanets–are distant worlds that are in orbit around stars far beyond our own Sun. Ever since the historic discovery of the first exoplanet a generation ago, literally thousands of others have been spotted by scientists on the hunt for such distant worlds. Some exoplanets MIGHTY Portable Vaporizer are bizarre; unlike anything ever previously imagined by astronomers, while others hauntingly resemble familiar planets in our own Solar System. In September 2014, astronomers using data collected from the NASA/European Space Agency (ESA) Hubble Space Telescope (HST), the Spitzer Space Telescope (SST), and the Kepler Space Telescope, announced that they have discovered yet another alien world wonder. This brave new world, dubbed HAT-P-11b is about the same size as our Solar System’s Neptune, and it has both clear skies and water vapor–making it the smallest exoplanet known on which water vapor has been detected. The results of this study appear in the September 25, 2014 issue of the journal Nature.
This discovery marks a new milestone in the scientific quest to eventually spot molecules in the atmospheres of smaller, rocky planets more akin to our own Earth. Clouds in the atmospheres of distant exoplanets can block the view of what is lying beneath them. The molecular composition of these lower regions can reveal precious new information concerning the history and composition of an exoplanet. Detecting clear skies on a Neptune-size world is a good indication that some smaller exoplanets might also have similarly good visibility.
“When astronomers go observing at night with telescopes, they say ‘clear skies’ to mean good luck. In this case, we found clear skies on a distant planet. That’s lucky for us because it means clouds didn’t block our view of water molecules, ” noted Dr. Jonathan Fraine in a September 24, 2014 Hubble Space Telescope Press release. Dr. Fraine is of the University of Maryland at College Park, and is lead author of the study.
An exoplanet is a planet that does not orbit our Sun, but instead orbits a different star, stellar remnant, or brown dwarf. More than 1822 exoplanets, dwelling in 1137 planetary systems–including 465 multiple planetary systems–have been detected as of September 12, 2014. There are also many free-floating exoplanets, not inhabiting the family of any stellar-parent at all, but doomed to wander lost and alone through interstellar space after having been evicted from their original planetary-systems–probably as a result of gravitational jostling by rude sister planets.
The highly productive Kepler mission space telescope has also discovered a few thousand candidate alien worlds, of which approximately 11% may be false positives. There is at least one exoplanet on average per star in our Galaxy. Approximately 1 in 5 Sun-like stars in our Milky Way are thought to be circled by an “Earth-sized” planet situated in the habitable zone of a parent-star. The habitable zone is that region around a star where the temperatures are not too hot, not too cold, but just right for liquid water to exist. Where liquid water exists, life as we know it may potentially exist, as well. The nearest exoplanet to Earth, that dwells within the habitable zone of its star, is thought to be within 12 light-years of Earth. Assuming that there are about 200 billion stars sparkling their way within our barred-spiral Milky Way Galaxy, that would mean that there are 11 billion potentially habitable Earth-like worlds, rising up to 40 billion if red dwarf stars are included in the calculations. Red dwarf stars are less massive than stars like our Sun, and they are the most abundant type of stars in our Galaxy. They also “live” for a very long time–perhaps trillions of years. In contrast, stars like our Sun “live” for about 10 billion years. If free-floating planets are also included in the count, this could potentially increase the number of possibly habitable worlds in our Galaxy into the trillions.
So far, the highly productive Kepler mission has detected over 1, 000 confirmed alien worlds, and flagged over 3, 000 candidates that still await possible confirmation by observations and follow-up studies. Kepler scientists think that at least 90% of these potential exoplanet candidates will ultimately be confirmed.
The first detection of an alien world in orbit around a Sun-like star came back in 1995–and it was a bewildering discovery. Named 51 Pegasi b (51 Peg b, for short), this immense, gas-giant sizzler was the very first hot Jupiter exoplanet to be detected by shocked astronomers. Hot Jupiters–a previously unknown class of planetary denizens of our Galaxy–hug their fiery parent-stars in extremely hot, “roasting” close-in orbits. Called “roasters”–for obvious reasons–before the discovery of 51 Peg b, astronomers had thought that gas-giant planets could only be born at much colder and greater distances from the sizzling hug of their searing-hot stellar parents. Before this historic discovery astronomers had believed that gas-giants could only form in the outer regions of their planetary systems–where Jupiter and Saturn dwell in our Sun’s own family. The four giant, gaseous inhabitants of our Solar System–Jupiter, Saturn, Uranus, and Neptune–are all situated in a frosty, dimly lit twilight region, far from the comforting warmth and glow of our Star.
HAT-P-11b is a so-called exo-Neptune– a planet of approximately the same size as our own Solar System’s Neptune in orbit around another star. It dwells about 120 light-years away in the constellation Cygnus (The Swan). Unlike the Neptune that dwells in our Sun’s own family, HAT-P-11b circles its star much more closely–Neptune is the most distant of the eight major planets from our Sun. Indeed, HAT-P-11b circles its star approximately every five days! It is a toasty alien world believed to harbor a rocky core, a mantle composed of ice and fluid, and a dense gaseous atmosphere. For a long time there was very little else known about the composition of this alien wonder world, and other similar exo-Neptunes–until now!
It is difficult for astronomers to analyze the atmospheres of exo-Neptunes, in part, because of their relatively small size. The considerably larger Jupiter-like exoplanets are much easier to detect and analyze. In fact, astronomers have already been able to discover the existence of water vapor in the atmospheres of some of these gigantic planets. However, smaller planets like HAT-P-11b, are more challenging to investigate–and all of the smaller ones observed, as of this writing, have appeared to be cloudy.
The team of astronomers used HST’s Wide Field Camera 3 and a technique termed transmission spectroscopy, in which an exoplanet is observed as it crosses in front of the fiery face of its parent star. Starlight filters through the rim of the transiting planet’s atmosphere and into the watchful eye of the observing telescope. If molecules like water vapor are present, they absorb some of the gleaming starlight, leaving distinct signatures in the light that reaches the telescope.
“We set out to look at the atmosphere of HAT-P-11b without knowing if its weather would be cloudy or not. By using transmission spectroscopy, we could use Hubble to detect water vapor in the planet. This told us that the planet didn’t have thick clouds blocking the view and is a very hopeful sign that we can find and analyze more cloudless, smaller, planets in the future. It is groundbreaking, ” Dr. Nikku Madhusudhan explained in the September 24, 2014 Hubble Space Telescope Press release. Dr. Madhusudhan is of the University of Cambridge in the uk, and is a member of the study team.
Before the team of astronomers could be truly confident about their new findings, they had to be certain that the water vapor was from the planet and not from cool starspots on the disk of its parent-star–which have been likened to “freckles” on stellar faces. Fortunately, Kepler had been watching the patch of sky in which HAT-P-11b happens to reside for years. Those visible-light data were then combined with targeted infrared SST observations. By comparing the datasets the astronomers were able to confirm that the starspots were too hot to contain any water vapor, and so the vapor detected must belong to the planet!
The results gathered from all three telescopes show that HAT-P-11b is covered in water vapor, hydrogen gas, and some other yet-to-be-determined molecules. In fact, HAT-P-11b is not only the smallest planet known to have water vapor in its atmosphere–it is also the smallest planet for which molecules of any kind have been directly discovered using spectroscopy. Scientific theorists will now be devising new models to explain the planet’s composition and origins.
Even though HAT-P-11b is termed an exo-Neptune, it is actually very different from any planet in our Sun’s family. Many astronomers believe that exo-Neptunes may have diverse compositions that result from their individual formation histories. New discoveries such as this can help astronomers put together a theory explaining the origin of these intriguing and remote alien worlds.
“We are working our way down the line, from hot Jupiters to exo-Neptunes. We want to expand our knowledge to a diverse range of exoplanets, ” commented Dr. Drake Deming in the September 24, 2014 Hubble Space Telescope Press release. Dr. Deming, a co-author of the study, is also of the University of Maryland.
The team of astronomers plan to study still more exo-Neptunes in the future, and they also hope to apply the same method to smaller super-Earths. Super-Earths are rocky, but more massive, kissing cousins of our own planet that can carry up to ten times the mass of Earth. Our Solar System does not harbor a super-Earth, but other telescopes are discovering them around other distant stars in immense numbers–and the upcoming NASA/ESA James Webb Space Telescope, currently scheduled for launch in 2018, will hunt for super-Earths, looking for signs of water vapor and other molecules. However, finding signs of liquid water oceans and potentially habitable alien worlds is still likely a long way off.
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