NASA’s Kepler Space Telescope is no stranger to media attention. It even made it into our top 10 physics events of 2015, so it should come as no surprise that the Kepler Mission is at it again, announcing on the 11th of May that it has discovered 1,284 new planets - the single largest finding of planets to date. What’s more exciting is that nine of those planets appear to be within the habitable zone of their parent star, an area with the right conditions to support life. We take a further look into this record-breaking discovery, and whether it answers the age old question: are we alone in the universe?
What is the Kepler Mission?
The Kepler Mission’s direct objective is to survey a specific region of the Milky Way to discover which stars host planets (also known as exoplanets), and of those exoplanets, which ones are in or near the habitable zone. The habitable zone is the region around a star in which water exists in all three states, allowing for life as we know it to form. This area of study has always been of interest to the human race, with astronomy in particular being one of the main focuses in science education.
- In particular, the Mission looks at many key elements within a planetary system, including:
- The percentage of terrestrial/larger planets within or near the habitable zone.
- The distribution or shapes and sizes of the orbits of these planets.
- The number of planets within a multiple star system (such as Kepler-453).
- The orbit size, planet reflectiveness, physical size, mass and density of short period giant planets.
- Ensuring the planets can be identified using other observational techniques to verify their existence.
- The properties of the stars harboring these planetary systems.
- To date, Kepler has identified 2,325 of the 5000 planet candidates that have been discovered. It is also the first mission to find potentially habitable, Earth-sized planets.
How Planets Are Discovered
For the past 4 years, Kepler has been monitoring 150,000 stars in a single patch of sky within our Milky Way in the hope of discovering something amazing. Using a method called transit photometry, the brightness of each star was monitored closely, and when a telltale dip in the brightness occurred, it was deduced that a planet had passed by, similar to someone standing in front of a lamp and causing a shadow.
But this method can only search so far. If we wanted to start exploring the universe beyond a few hundred light years, a method known as Microlensing holds some promise. This method analyzes how the gravity of one star affects the gravity of another, causing the light from the primary star to bend around the other. If the primary star is behind the secondary star, a ring of light will appear, resulting in a dramatic increase in light. If a planet is present, a temporary spike in brightness will also occur for a short amount of time (hours to days). This is a telltale sign of a planet being present, and can be used to detect planets as far as 22,000 light years away. It also gives much more precise information on the size and mass of the planet. However, even this method has its limitations, as these events only happen once, so if you miss your window, you miss the opportunity altogether. For this reason, scientists employ more common methods, such as Doppler Spectroscopy.
Kepler also used some intense software to help rule out false positives - statistical results that appear to be accurate when in fact they are not. Since scientists were only viewing a small portion of the sky, it is very easy to get measurements from different planetary systems interfering with the source you are trying to observe. Timothy Morton, associate research scholar at Princeton University in New Jersey and lead author of the scientific paper published in The Astrophysical Journal, was part of the team who used this large-scale computation, the first of its kind. In terms of the statistical analysis performed on the data, he explained that,
"Planet candidates can be thought of like breadcrumbs; if you drop a few large crumbs on the floor, you can pick them up one by one. But, if you spill a whole bag of tiny crumbs, you're going to need a broom. This statistical analysis is our broom."
Searches like this allow scientists to gather a large database of planets in which to begin the search for extraterrestrial life. It is just one of the many ingredients needed to be as informed as possible on our surroundings in the universe. This provides scientists with a starting point so they can establish which planets are more likely to harbor life, allowing for more thorough investigations. The technology to do this only became available recently, so it will be a little while before predictions can be fully supported with other signatures of life.
The 9 Habitable Planets
Of the 1,284 planets the Kepler Mission identified, 550 of them are thought to be rocky based on their size, and 9 of them reside in the habitable zone of their parent star. These new additions join 12 other habitable exoplanets, bringing the grand total of discovered, potentially life-harboring planets to 21. Unfortunately, this does not guarantee that life exists there. Other features must be identified first before any conclusions can be drawn. How much radiation the planet emits (this is where an ozone layer is important), the chemistry of the planet, and whether the surface is affected by solar flares are all features that can severely impact whether a technically “habitable” planet is suitable to harbor life. Scientists hope that future telescopes will be able to pick up such events, and hopefully identify key signatures of life such as oxygen, water, carbon dioxide and methane.
This sort of information, along with the other results from the Kepler Mission, help decide what should be done on upcoming journeys into space.
What is Kepler up to now?
October of 2017 will see the end of the Kepler mission, including the production of the final discovery catalog. This comes after some malfunctioning that occurred on the craft in 2012 and 2013, which meant that it could no longer hunt for planets using the usual approach.
In the meantime, the K2 Mission, which was a new mission plan for Kepler’s remaining functional capabilities, took over in 2013, which searched a much larger area in the plane of Earth’s orbit around the Sun. It was launched in 2014 to extend Kepler’s legacy, and will run until 2018.
In 2018, a new satellite will be launched called the NASA Transiting Exoplanet Survey Satellite (TESS), which will focus on 200,000 bright nearby stars and search for Earth, and Super-Earth sized planets. TESS will survey 400 times as much sky space as any other similar mission, focusing more on planets closer to Earth than the original Kepler Mission. It will also monitor 50,000 more stars than Kepler, increasing the chances of a habitable planet being found.
Other future plans to explore these planets include the James Webb Space Telescope and the High Definition Space Telescope, both of which will look more closely at the planets and their atmospheres to directly search for signs of life.
What does this mean for us?
Although the technology to confirm life on other planets resides in the distant future, the odds of other life in the universe continues to increase with each new discovery by Kepler. Are we alone in the universe? Statistically speaking, probably not. But the real question for humanity is: are we ready to know that answer?
Featured image credit: NASA/W. Stenzel
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