NASA Telescope Discovers More than 2,600 New Alien Planets
On March 7, 2009, NASA launched the Kepler space telescope into orbit around the Sun. Outside the Earth’s atmosphere, it would be free to peer deeply into a cross-section of our galaxy in search of new planets orbiting other stars.
After nine years in action covering two separate mission phases (designated as Kepler and K2), the Kepler space telescope finally ran out of fuel and was forced to cease operations in October 2018. But over the course of its lifespan, it discovered more than 2,600 new planets, at least a few of which may be capable of supporting life.
In addition to the 2,681 objects already classified as exoplanets (planets outside the solar system), the U.S. space agency listed another 2,899 candidates for planetary status that have yet to be verified, and a positive result is expected for most. As of 2015, the data from the initial Kepler mission (K2 data was not yet available) had confirmed the existence of 30-50 Earth-sized planets known to be orbiting inside their star’s “habitable zone,” which means temperatures would allow for the existence of water on the surface.
“As NASA’s first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond.”
These were the words of Thomas Zurbuchen, the associate administrator of NASA’s Science Mission Directorate in Washington, marking the occasion of Kepler’s official retirement from active duty.
In the wake of Kepler’s performance, it can now be confirmed that there are more planets in the Milky Way galaxy than stars. This means our solar system is one of only many in our cosmic neighborhood.
Surveying the Cygnus Constellation
When Kepler was launched into orbit, its measuring devices were programmed to focus on a section of the sky in the constellation Cygnus, which is located on the plane of the Milky Way. For the first three years of its existence, the Kepler space telescope collected data while observing approximately 150,000 main sequence (active and still in the prime of their lives) stars located in that area.
The Kepler was searching for small dips in brightness of the light emitted from these stars, which would occur whenever a planet in orbit passed across a star’s face. The size, composition and orbital distance of these planets could be inferred from these observations.
This is a reliable method for discovering exoplanets (planets outside our solar system), and the Kepler performed its mission ably for three years. Unfortunately, in the summer of 2012 it experienced significant mechanical failures, as two of the wheels in its orientation system failed. This made precise control of the Kepler’s instrumentation impossible, which for a while put the entire mission at risk.
All activity on the Kepler was halted as NASA scientists mulled over their options. Eventually they did find a solution that kept the Kepler in commission, and at that point its original mission was officially terminated.
While the end for Kepler’s initial mission came more quickly than expected, its quest still proved highly fruitful. According to figures released by NASA in 2017, the final tally for Kepler’s survey of the sky in the Cygnus constellation was 4,034 planetary candidates discovered (including 50 with Earth-like characteristics orbiting in habitable zones) and 2,335 new planets confirmed (including 30 of the 50 Earth-like candidates).
These numbers mean that between 1-2 percent of the planets found resembled Earth, in size, composition and location. This may not sound overly impressive, but it must be remembered that we live in a Milky Way galaxy that contains somewhere between 100 billion and 400 billion stars, with a population of planets that far exceeds these totals. If only one percent of the existing planets was Earth-like it would mean billions of Earths were orbiting stars in our very own galaxy, which is only one of 100 billion galaxies believed to exist in the known universe.
K2: A New Directive
When Kepler lost its ability to orient continuously toward Cygnus, its assignment was changed. Instead of looking in one direction, it was allowed to change its focus as it moved around the Sun.
New regions of the sky were scanned every few months, in a search for relatively brighter and closer stars and planets. The initial Kepler mission had been looking primarily for dim stars and distant planets, but during K2 the telescope was re-purposed to help NASA fill in the gaps and contain a more complete picture of what might be out there.
From 2015 through 2018, the Kepler space telescope continued to perform its duties admirably. By the time its mission ended, the final count for the two Kepler missions combined was over 5,500 exoplanet candidates, either verified or likely to be verified in the future.
In its planetary catalog, the Kepler space telescope found quite a few gas giants (like Jupiter or Saturn in our solar system), which are made primarily of hydrogen and helium and are sometimes referred to as failed stars. It also uncovered many ice giants (like Uranus and Neptune), which contains heavier elements like oxygen, carbon and nitrogen in frozen or liquid form.
However, the most common type of planet found belonged to a category unfamiliar to our solar system. These are planets with rocky cores that mostly fall into a size range somewhere between Earth and Neptune (roughly between 15,000 and 45,000 kilometres in diameter).
Interestingly, the vast majority of these planets are somewhat larger than Earth or somewhat smaller than Neptune, with not much representation between these two subcategories. For reasons that currently baffle planetary scientists, it appears the Neptune-like planets were originally in the Earth size range but swelled up like balloons after absorbing small amounts of hydrogen and helium.
The Endless Search for Life as We Know it … and Don’t Know it
The total number of Earth-like planets found in habitable zones by Kepler was not that high (the final number will likely be somewhere in the low hundreds). But they are common enough to suggest that we are far from unique.
Based on statistical projections, planetary scientists examining the Kepler data estimate that between 20 and 50 percent of the stars in our galaxy have small, rocky planets in the Earth size range revolving in their habitable zones. Essentially, this means these planets would experience temperatures moderate enough to allow liquid water to flow across their surfaces, which would likely encourage the evolution of life.
While NASA’s focus on finding Earth-like planets in so-called habitable zones is understandable, other worlds might also be capable of supporting life. Some scientists theorize that moons or planets orbiting stars outside the habitable zone could function as crucibles for evolutionary processes, if they have oceans or lakes either underground or beneath icy surfaces. Mars and Jupiter’s moon Europa are two bodies in our solar system that fit this description, and according to experts both may be inhabited by microbial life (or by something even larger).
William Borucki, the space scientist from NASA’s Ames Research Center who was listed as the principle investigator on the Kepler project, acknowledged the importance of finding planets with similar characteristics and histories as Earth.
But he also noted that Kepler had “discovered planets completely unlike those in our solar system. Some of those, in fact, might be actual water worlds. We’ve also found planets that were formed at the beginning of the formation of our galaxy, six-and-a-half billion years before the formation or our own star and before the formation of the Earth. Imagine what life might be like on such planets.”
In April 2018, NASA launched its latest space telescope, the Transiting Exoplanet Survey Satellite (TESS). This next-generation instrument will scan an area of the sky 400 times bigger than the area covered by Kepler, and its projected to find as many as 20,000 new exoplanets.
With such a massive collection of data, surprises are bound to be uncovered. The way we think about the universe and about the possibilities of life elsewhere will likely continue to evolve, as this relentless search for information intensifies.
Top image: Alien planet with double moon over crater. Credit: Phil Daub / Adobe Stock
By Nathan Falde