Tuesday, July 26, 2011

Digesting the Exoplanet Search

I've received a couple of emails asking me to explain what the situation with the exoplanets is. There have been various conflicting reports about discoveries of Earth-like planets. This is my attempt to digest, in a concise manner, what the exoplanet search is all about, what we have achieved as of now and what we will achieve in the coming years.

Exoplanet or Extrasolar planet is simply a planet that is located outside of our Solar System. We had always assumed that there were other planets orbiting 200-400 billions of stars in our Galaxy, however detecting them remained a hopeful dream until the 1990's. The problem with detecting a planet, other than the requirement of extremely powerful telescopes, is their proximity to the host star. When we look at another star system, all we see is the intense light (energy) given off by that star. Thus, we cannot look at the exoplanets in the same way that we look at the planets in our Solar System.

                                          Exoplanetary vision. Credit: NASA  

However, by the 1990's scientists devised several ingenious ways of detecting planets orbiting around other stars. Instead of trying to see the planets themselves, what we do is study the relationship between a hypothetical planet and its host star. In using Radial velocity method, for instance, scientists looks for the slightest gravitational pull that a planet exerts on its host star. The transit method is utilized to detect exoplanets that are transiting (orbiting) in front of the star, in its relation to us. When a planet passes right before its star, the light output which we observe is slightly less than when there is nothing in front of it. Direct imaging method is, for now, limited to seeing gigantic and extremely bright planets.

                                          Exoplanetary vision. Credit: NASA

The hunt for exoplanets was on. It intensified about 10 years ago, when ever more Astronomers joined in, spending years of observations to successfully prove an existence of yet another alien world. Most of these planets were hot Jupiter-like gas giants, because they are the easiest to detect. They are interesting to study, but fail to satisfy our curiosity for finding planets that are exactly like Earth. We wondered, in these early exoplanet hunting years, whether we will ever find a twin of our small blue dot (Carl Sagan)

Then everything changed when NASA launched into space the Kepler Telescope in 2009. It was designed specifically to hunt for Earth-like planets in a particular region of the Milkyway galaxy. It utilizes a transit method to search for exoplanets among, approximately, 9 million stars. This is a large enough group of stars to allow us to speculate on the frequency of presence of various types of planets in the entire galaxy. The Kepler, however, is yet to confirm its extrasolar planetary bounty of detected planets, because a solid confirmation requires years of observations. Just like Earth orbits around the Sun in a year, other planets need to pass in front of their stars for observations to be complete and accurate. As of now we know of Kepler's extrasolar planetary candidates, not all of which are going to be confirmed. Many have rushed to use this data for premature conclusions.

The Kepler mission, as of July 26, 2011 has confirmed discovery of 17 exoplanets and 1235 exoplanet candidates. Five of the candidate planets are of Earth-size and are in habitable zones. When we say an Earth-like planet, we mean a planet of similar size, rocky composition, as opposed to gaseous, orbiting in its host stars habitable zone. Essentially, the conditions required for a planet to be able to sustain liquid water on its surface. 49 more planet candidates in habitable zone are larger than Earth, ranging from the so-called Super-Earth size (twice as big) to planetary giants like our local Jupiter. We just have to wait for final confirmations before opening a bottle of champagne. This will take a few more years.

Ground based observations have produced over 550 confirmed exoplanets as of 2011, with an accelerating pace of discoveries from one year to another. One planetary system persists to stand out of all, it is Gliese 581, located just over 20 light-years away from Earth. It appears to share some remarkable similarities with our own system. A habitable zone is an orbital distance from its host star where conditions favorable to liquid water can exist. In our Solar System we have Venus that is just on the edge of habitable zone, being too hot, with a runaway greenhouse effect, Earth right within the habitable zone and Mars on the outer edge of it, being slightly too cold. Gliese 581 system appears to have the same three type of planets, Gliese 581 c is on the inner edge, Gliese 581 g is right in the middle of it and Gliese 581 d. 

When scientists announced in September of 2010 their discovery and confirmation of the existence of Gliese 581 g planet, it became the first Earth-like world known to us besides our own planet. It is a fascinating, alien world, that is tidally-locked, always facing its star with one side, with the other always remaining in the dark. The terminator line, between both sides, is where Earth-like conditions could exist. Soon, however, controversy was revealed when many in the scientific community concluded that the data was insufficient for a confirmation and the planet was relegated to a candidate status.

Comparison of the Solar System with the Gliese 581 system. The blue line represents the habitable zone. Credit: European Southern Observatory. 

This is where the search for Earth-like planets stands today. We have confirmed existence of over 563 planets, including 53 planetary system with at least two planets. The overall scientific consensus, however, is that there is not a single Earth-like confirmed exoplanet yet. The very existence of Gliese 581 g (also known as the Zarmina planet) is put into question, although many are advocating that the conducted observations were sufficient. Either way, it is very likely that NASA's Kepler space-based telescope will confirm an Earth-like exoplanet within a year or two.

Thank you for reading, don't forget to subscribe and check out the official main project site: www.SpaceChronology.com

Wednesday, July 20, 2011

Possible signs of life on Mars

Life on Mars is one of the oldest ideas about outer space that caught the public's attention. No other planet has been depicted so often and often in such an incorrect manner as Mars did. Our perception of the red neighbor has changed dramatically within the last 100 years. We went from almost certain conviction that intelligent being could live there, strangely they were always very reminiscent of our own species, to an understanding that nothing at all could live there, not even the most primitive of life forms. The latter idea gained dominance after two American exploration probes, Viking 1 and Viking 2, landed on Mars in 1976. As first pictures were transmitted to Earth and examined by the NASA scientists, Mars seemingly offered us nothing but a desolate frozen landscape. Interest in the red planet dwindled in the 1980's and in the early 1990's.

Lately, however, we have established a near-permanent presence, both above the planet, in the form of orbiters and on the ground, in a form of the famous rovers. In 1997 a little NASA Pathfinder rover opened up Mars to decades of intensive exploration. In 2004 now almost celebrity-like Opportunity and Spirit rovers landed on Mars and exceeded all expectations as to their expiration dates. Instead of the planned 3 month missions, Spirit went on to work for another 6 years and Opportunity is still, against all odds, exploring the mysterious world next door. In 2012 it will be joined with the Curiosity rover, a remarkable machine representing the very pinnacle of our technological advancement.

The more we explored Mars, the more interesting it seemed to get. We don't view it with naive optimism of the early days of the 20th century, nor do we share the pessimism of the scientific community of the 1970's. Instead, we see Mars as a real world, whose history we now understand, to some extent. We know that some 3-4 billions of years ago Mars had warm bodies of flowing water on its surface. We know that in the past there existed conditions on the surface of Mars suitable for life to emerge and to exist for relatively long periods of time. It had a thicker atmosphere. Just underneath the martian sand there are minerals that are formed, at least on Earth, exclusively with prolonged contact with warm, liquid water. We do not yet know whether there was life on Mars in the past, but there is circumstantial but tantalizing evidence of biological processes today.

There is an area on Mars where methane gas is released cyclically, following seasonal changes. It must be coming from underground because there is otherwise no indication of any abnormal activity on the surface of that area.On Earth most of methane gas is produced by living organisms and some is a byproduct of geological activity. In either case, it means that Mars has yet to exhale its last breath, figuratively speaking.

Astrobiologists found extremophile bacterial organisms on Earth that could survive and thrive on Mars. This means that not only could there have been life in the past, but that it could still survive there, in a highly primitive form.

NASA is executing and planning many exciting missions to explore Mars, a world that refuses to ease its firm grip on our monkey curiosity. Next year stay tuned for Curiosity's arrival. European Space Agency is also contributing to the exploration in the form of Mars Express, an orbiter examining martian surface in great detail. In the future NASA intends to even send an airplane that will fly over the area of methane gas intrigue, collecting data that is otherwise impossible to obtain from the orbit in space.

Tuesday, July 12, 2011

What is the state of current space exploration?

With the retirement of the space shuttle fleet there is a substantial amount of misunderstanding and confusion among the general public. Many think that it marks the demise of NASA and of space exploration in general. However, this is inaccurate and I will try to set the record straight. 

What is space exploration? Seeking and discovering new scientific data that broadens our horizons, quite literally. NASA has no competition in the world and the distant second is European Space Agency with JAXA (Japenese Space Agency) a third, in some sense. Mankind explores outer space in two ways: sending  probes and space telescopes. The latter are used primarily to answer big astronomical questions about our place in the Universe, while the former is currently limited to the Solar System. We have several prominent missions both ongoing and soon-to-be-launched. The Kepler space telescope is one the most ambitious mission in the history of humanity, so far, in terms of seeking out worlds (planets) outside our Solar System. We have New Horizons probe rushing towards the Kuiper Belt, specifically Pluto and its moons. Most advanced robotic rover ever conceived is going to be launched to the Red Planet this year and the Dawn spacecraft has begun its three-month long orbit insertion in the Asteroid Belt, which will not only open up two almost entirely known worlds, known as Vesta and Ceres, but also reveal the processes of planet formation.

You can learn about these and other missions in the official SpaceChronology.com website. 

But what was the role of the space shuttle fleet? You may ask. It is an orbit delivery system, to get cargo, mainly satellites and astronauts into space. Astronauts work on the International Space Station where we learn how to live in space, which is crucial to our long term space colonization prospects and intentions. These missions are what is known as manned space program. However, NASA is still building rockets to send probes and deliver space satellites into outer space. Building rockets is not cutting edge technology anymore, in fact private companies will soon take over this task, think of them as space taxis, they get equipment where it needs to go. Until that happens NASA is going to hitch a ride on cheap Russian rockets and Soyuz-spacecraft which have been in use since the 1960's. 

Even though the taxi is temporarily of foreign origin, NASA is still conducting the bulk of space exploration and this is not likely to change in the coming decades. Those of you who were worried that space exploration is being somehow terminated, don't worry, it isn't 

There is, however, a danger of the next generation cutting-edge unprecedented awe-inspiring James Webb Space Telescope being terminated due to pending budget cuts in the U.S. House of Representatives. If you are concerned about the future of space exploration, please contact your Representative and Senators to express your concern, urging them to vote against termination of the JWST project. This is by far the most important project in Astronomy and will benefit humanity for decades to come.