FREE NEWSLETTER: Econintersect sends a nightly newsletter highlighting news events of the day, and providing a summary of new articles posted on the website. Econintersect will not sell or pass your email address to others per our privacy policy. You can cancel this subscription at any time by selecting the unsubscribing link in the footer of each email.

posted on 12 May 2016

More Than 1,000 New Exoplanets Discovered But Still No Earth Twin

from The Conversation

-- this post authored by Andrew Norton, The Open University

NASA astronomers working with data from the Kepler space observatory have presented the largest single crop of newly discovered exoplanets to date. It's impressive - 1,284 new planets have been announced, including around 550 which are of comparable size to the Earth. However just nine of these may be in their stars' habitable zones - where it is plausible that liquid water could exist on the surface of a planet.

Kepler discovers planets by looking for a tiny dip in light as a planet passes across the face of its parent star, blocking a fraction of the starlight. This so-called transit is exactly the same phenomenon as many of us witnessed on May 9 with the transit of Mercury across the face of the sun. But, unlike Mercury or Venus, which we can see from Earth when they transit the sun, astronomers cannot image an exoplanet or even its star as anything other than a point of light, simply because they are so far away.

For an exoplanet similar to Jupiter the dip in light can be as much as 1% of the star's brightness, and measuring such dips has been routine for a decade with ground-based telescopes such as SuperWASP. The advantage of Kepler, which is in space, is that it can measure the tiny dips due to Earth-sized planets - which may be up to 100 times smaller still. Even so, transits are only visible from those systems aligned edge-on to our line of sight; for every transiting exoplanet found, there will be hundreds more that cannot be detected.

Not everything that looks like a transit really is an exoplanet. Sometimes a bright single star is aligned with a fainter "eclipsing binary" - a pair of stars orbiting their common centre of mass such that each passes in front of the other, blocking a large fraction of the total light. On its own, the eclipsing binary may produce deep eclipses that are clearly distinguishable from transits, but when the light is diluted by the single star lying along the same line of sight, the result can look like an exoplanetary transit. These are known as "false positives".

So Kepler spots a huge number of "candidate" exoplanets (known as Kepler Objects of Interest), but they remain candidates until confirmed in some other way.

Artist's impression of Kepler in action. NASA

The only way astronomers can be certain they have a planet and not something else is to measure its mass, and that can be done in two ways. If the system contains multiple transiting planets, astronomers can look for timing variations as the planets tug each other through their mutual gravitational attraction. This can be used to work out the masses of the individual planets. Alternatively, astronomers can analyse the light from the star to observe the Doppler shift in its spectrum - the starlight is periodically red-shifted and blue-shifted by a tiny amount as the unseen planet orbits the star, tugging it to and fro, and the shift in wavelength depends on the planet's mass.

The problem with the vast majority of the unconfirmed exoplanets is that they are not in multiple planetary systems and they are orbiting stars that are too faint to measure their Doppler shift. Instead, astronomers have to rule out the false positives by other means. That is precisely what the Kepler scientists have done.

The team ran computer simulations of real exoplanetary transits to quantify how much like a transit each observed signal appears to be. They then ran other simulations of objects that can mimic transits and used those to work out how common imposters would be that could mimic the signal observed. This gave them a probability of the observed signal being due to an exoplanet.

The team analysed 4,302 candidate planets from a list published by the Kepler team in July 2015. They concluded that 1,284 of them have a 99% chance or better of being exoplanets; another 1,327 of them are more likely than not to be exoplanets, but more work is needed to confirm them. That leaves 707 objects which are likely to be due to something else and 984 which have already been verified as exoplanets by others, and which this study has confirmed.


From the newly identified sample, around 550 are smaller than twice the radius of the Earth, which means they could be rocky in composition. Nine of these lie in the optimistic habitable zone around their stars. However, six of the nine lie on the extreme inner edge of the habitable zone and another lies on the extreme outer edge. This leaves just two firmly within the "conservative" habitable zone and only one of these - the exoplanet Kepler 1229b - is similar in size to the Earth at 1.1 Earth radii. However, even that is not in an Earth-like orbit, as its parent star is a cool red dwarf which the planet orbits once every 87 days.

An artist's impression of what planet Kepler-452b may look like, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. NASA Ames/JPL-Caltech/T. Pyle

An Earth-sized planet is considered to be one with a radius between 0.7 and 1.2 times that of the Earth. Exoplanets with radii in the range 1.2 to 1.9 Earth radii are referred to as "super-Earths" and those with radii between 1.9 and 3.1 Earth radii are called "sub-Neptunes". The surprising thing is that around two thirds of all the planets discovered by Kepler are in these latter two categories. Strangely, we see no planets of this size in our own solar system - here everything is either Earth-sized or smaller or it is Neptune sized or larger.

Earth-sized planets are certainly harder to detect than super-Earths or sub-Neptunes, but the fact remains that astronomers have not yet found an Earth twin. Such a planet would have not only a radius similar to the Earth but a mass similar to the Earth too (and so presumably a similar bulk composition) and it would orbit a star of similar mass, size, luminosity and temperature to the sun in an orbit that takes around a year to complete.

The latest announcement is an impressive piece of work, and the discovery of so many new exoplanets is stunning. It is increasingly clear that planets orbit stars as a rule - not an exception. While astronomers still haven't found an exact twin of the Earth, the rapid pace of discoveries is surely a sign that it is just a matter of time until they do.

The ConversationAndrew Norton, Professor of Astrophysics Education, The Open University

This article was originally published on The Conversation. Read the original article.

>>>>> Scroll down to view and make comments <<<<<<

Click here for Historical News Post Listing

Make a Comment

Econintersect wants your comments, data and opinion on the articles posted. You can also comment using Facebook directly using he comment block below.

Econintersect Contributors


Print this page or create a PDF file of this page
Print Friendly and PDF

The growing use of ad blocking software is creating a shortfall in covering our fixed expenses. Please consider a donation to Econintersect to allow continuing output of quality and balanced financial and economic news and analysis.

Take a look at what is going on inside of
Main Home
Analysis Blog
Why Long-Run Theories of Profit and Accumulation Fall Short
Brexit - Who Wins and Loses
News Blog
What We Read Today 25 April 2017
April 2017 Chemical Activity Barometer Suggests Continued Growth Through 2017
Final April 2017 Michigan Consumer Sentiment Slips but Remains Strong
Richmond Fed Manufacturing Survey Again Improves In April 2017.
March 2017 Headline New Home Sales Improve and Above Expectations
Case-Shiller 20 City Home Price Index February 2017 Shows 5.9 % Year-over-Year Growth
Infographic Of The Day: Comparison Of Population Density
Early Headlines: Asia Stocks, Dollar, And Oil All Up, Gold Down, China Stocks Diverge, Bankrupt Retail, Courtiers To Palace Wed., US Starts Trade War With Canada Over Lumber, And More
April 24, 2017 Weather and Climate Report - All Too Normal!
The Countries With The Fastest Internet
CO2 Levels And Global Warming
Worthless Mining Waste Could Suck CO Out Of The Atmosphere And Reverse Emissions
Average Gasoline Prices for Week Ending 24 April 2017 Rose Over 1 Cent
Investing Blog
Irrational Exuberance From France
The Real 401k Plan Manager 24 April 2017
Opinion Blog
Reducing Inequality Could Be A Matter Of Survival
America's Gilded Age 2: On The Rocks
Precious Metals Blog
Three Gold Plays For The New Era Of Chaos
Live Markets
25Apr2017 Market Close: Nasdaq Pushes Above 6,000; Dow Broke 21k Before Pulling Back; Dollar And Gold Slide While Oil Advances
Amazon Books & More

.... and keep up with economic news using our dynamic economic newspapers with the largest international coverage on the internet
Asia / Pacific
Middle East / Africa
USA Government



Analysis Blog
News Blog
Investing Blog
Opinion Blog
Precious Metals Blog
Markets Blog
Video of the Day


Asia / Pacific
Middle East / Africa
USA Government

RSS Feeds / Social Media

Combined Econintersect Feed

Free Newsletter

Marketplace - Books & More

Economic Forecast

Content Contribution



  Top Economics Site Contributor TalkMarkets Contributor Finance Blogs Free PageRank Checker Active Search Results Google+

This Web Page by Steven Hansen ---- Copyright 2010 - 2017 Econintersect LLC - all rights reserved