The Special Ingredients of Earth
March 18, 2016: With its blue skies, puffy white clouds, warm beaches and abundant life, planet Earth is a pretty special place. A quick survey of the solar system reveals … nothing else like it.
But how special is Earth, really?
One way to find out is to look for other worlds like ours elsewhere in the galaxy. Astronomers using NASA’s Kepler space telescope and other observatories have been doing just that. In recent years they have been finding other planets increasingly similar to Earth—but still none that appear as hospitable as our home world. For those researchers, the search goes on….
Another group of researchers have taken an entirely different approach. Instead of looking for Earth-like planets, they have been looking for Earth-like ingredients. Consider the following:
Our planet is rich in elements such as carbon, oxygen, iron, magnesium, silicon and sulfur—the stuff of rocks, air, oceans … and life.
Are these elements widespread elsewhere in the universe? To find out, a team of astronomers led by Aurora Simionescu, an astrophysicist at the Japan Aerospace Exploration Agency (JAXA) in Sagamihara, Japan, used Suzaku, a Japanese X-ray satellite with NASA participation, to survey a cluster of galaxies located in the direction of the constellation Virgo.
The Virgo cluster is a massive swarm of more than 2000 galaxies, many similar in appearance to our own Milky Way, located about 54 million light-years away. The space between the member galaxies is filled with a diffuse gas so hot that it glows in X-rays. Instruments onboard Suzaku were able to look at that gas and determine which elements it is made of.
Reporting their findings in the Astrophysical Journal Letters, Simionescu and her colleagues reported findings of iron, magnesium, silicon and sulfur throughout the Virgo galaxy cluster.
Simionescu says “The elemental ratios are constant throughout the entire volume of the cluster and roughly consistent with the composition of the sun and most of the stars in our own galaxy.”
When the Universe was born in the Big Bang 13.8 billion years ago, elements heavier than carbon were rare. These elements are present today mainly because of supernova explosions. Massive stars cook elements such as carbon, oxygen, iron, magnesium, silicon and sulfur in their hot cores and then spew them far and wide when the stars explode. According to the observations of Suzaku, the ingredients for making sun-like stars and Earth-like planets have been scattered far and wide by these explosions. Indeed, they appear to be widespread in the cosmos.
"The elements so important to life on Earth are available, on average, in similar relative proportions throughout the bulk of the universe," adds Simionescu. "In other words, the chemical requirements for life are common."
Earth is still special. But according to Suzaku, there might be other special places, too. Suzaku recently completed its highly successful mission. On February 17, 2016, JAXA launched a follow-up mission to continue the survey: Hitomi, previously named ASTRO-H before launch, is a Japanese-led observatory carrying a key NASA instrument. The observatory will extend such studies to clusters of galaxies far beyond Virgo.
For more news from the distant corners of the cosmos, stay tuned to science.nasa.gov.