The study of exoplanets is without any doubt the most active and disrupting field in today astronomy. I had often blogged about it since it is my little obsession. Unfortunately, I have a hard time to keep up with the amount of discoveries and announcements being made every week over the past 3 years. This post is a snapshot of the recent study of exoplanets: what we know, what have been recently discovered and what is coming soon.
Today (May 2 2012) the Extrasolar Planets Encyclopaedia lists the characteristics of 763 exoplanets. Exoplanet App contains 760 discovered exoplanets. The NASA Planet Quest web site is slightly less optimistic with 691 confirmed exoplanets plus 2,321 potential candidates. These differences come from the lack of consensus about the definition of an extrasolar planets (or “exoplanets”) and also, the criteria used to confirm the genuineness of a discovery (e.g. the debate about Fomalhaut b). Nevertheless, with almost ~800 exoplanets known today, we have enough data to say that:
They are everywhere. Some of them orbit around one star identical to our sun, others have two sunrises and sunsets since they circle around compact binary star systems (also called circumbinary planets), or float alone in space (“nomad planets” which have been ejected from their planetary system). Astronomers even think that they have detected exoplanets from other galaxies (extragalactic exoplanets).
They are plentiful. A recent study showed that there are more than 1 exoplanets per star in our galaxy. Our galaxy is made of 200 billion of stars so that’s a lot of worlds out there, Giordano Bruno was right.
Young, old or ancient planetary systems, they are here. The youngest one was discovered around a recently-born star (100 million year old). The oldest one, nicknamed “Methuselah” which is 12.7 billion years old (almost 3 times the age of our sun), orbits around remnants of stars (a pulsar and a white dwarf). Recently, astronomers find exoplanets which survived the red giant phase of their star, giving us a hint of the future of the solar system.
They could be similar to our solar system planets. Several Earth-size planets were found recently (e.g. Kepler-20). Kepler NASA early results suggest that most of the exoplanets are in fact Neptune-sized or smaller planets. Recently, a group of astronomers claimed to have discovered a Saturn-like exoplanet (an exoplanet with rings).
They could host life. Astronomers found exoplanets very close to their host star, with temperature so high that the rocks can melt forming a global volcanism on the surface and a comet-like appearance. In contrast some planetary systems host distant (>200 AU), so probably frozen, exoplanets. Between those extremes, it exists a region around each star where liquid water can be maintained if a terrestrial exoplanet, or one of their moons, have a significant atmosphere. Several known exoplanets have been discovered in this so-called Habitable Zone and astronomers claimed recently that they could be billions of them based on the study of frequency of exoplanets around M-type stars. Unfortunately we don’t have yet the instruments to detect life on those exoplanets, but it will happen in the future with the new largest telescopes being built on the ground (e.g. TMT) and in space (e.g JWST).
Predicting the future: What discoveries are coming soon?
A search for extrasolar moons (or “exomoons”) have been initiated recently by several groups using the large amount of data provided by the Kepler NASA telescope. Two exoplanets have been already suspected to possess an exomoon, but no clear evidence has been published yet. The year 2012 might be the year when one of these teams announces the discovery of an exomoon.
More exoplanets will be imaged, and thus better characterized, thanks to the availability of instruments specifically built for this task such as SPHERE for one the VLTs (end of 2012), GPI of the Gemini South Telescope (end of 2012) and SCExAO of the Subaru Telescope (2012). These instruments will provide an image and a spectrum in the near-infrared of young gaseous exoplanets allowing us to know that they exist, but also to get an idea of their orbit, composition, temperature, and size.
An Earth 2.0, an Earth-like exoplanet in orbit in the habitable zone of its sun-like star, is without any doubts the Holy Grail of this field of astronomy. We don’t have yet the capability to directly see such exoplanet, but the Kepler spacecraft, which has been observing ~160,000 stars over the past three years may have already detected 3 transits of an Earth twin. If this planet exists, we will soon hear about it and it will hopefully motivate us to seriously start building the next generation of instruments capable of collecting an image of an Earth-like exoplanet.
These discoveries will expand our knowledge about exoplanets and will also radically change the vision of our sun neighborhood and our place in the universe. Imagine that in a few years while starring at the bright stars in the sky, you will be capable of telling as well which ones possess one or several exoplanets and if their world are suitable for life as we know it. Hopefully, by then, we will have decided to give real names to these nearby worlds, something more romantic and attractive than “b”, “c”, “d”,…
While you are waiting for these great discoveries, you can start dreaming about these new worlds by checking out the artistic impressions of exo-worlds on my Pinterest board.
Writing this post, I kept being amazed by the radical change in the field of astronomy that I witnessed over the past 5 years. I could not avoid thinking about what I could be writing in this blog about exoplanets in 5 years. This is without any doubt the most exciting field of astronomy.
Franck M. It’s all About