Key Building Block For Life Discovered In A Planet-forming Disk
CfA astronomers have helped discover rare types of methanol, a building block required for life as we know it to form.
Astronomers have found a rare form of methanol, a type of alcohol, in a planet-forming disk, providing a critical step in understanding how life beyond Earth may form. This result reveals vital details about the chemical composition of the ice in disks that form planets, and what organic molecules are available for comets to deliver to planets, including in our Solar System.
While astronomers have found evidence for other more complex molecules in planet-forming disks around other stars, this latest discovery is the first time that rare isotopes of methanol have been detected. Isotopes are different versions of a chemical element or compound that have the same numbers of protons but different numbers of neutrons.
“Finding these isotopes of methanol gives essential insight into the history of ingredients necessary to build life here on Earth,” said Alice Booth of the Center for Astrophysics | Harvard & Smithsonian (CfA) who led the study.
Booth and colleagues discovered these isotopes of methanol around HD 100453, a star with about 1.6 times the mass of the Sun located about 330 light-years from Earth. They used data from the Atacama Large Millimeter-submillimeter Array (ALMA), an international radio array in the Atacama Desert in Chile supported by the National Science Foundation in the US.
Scientists, like this research team and many others, look at planet-forming disks around stars as laboratories because they reveal the amounts of complex organic molecules that are present when planets and comets are assembling.
“Finding out methanol is definitely part of this stellar cocktail is really a cause for celebration,” said co-author Lisa Wölfer of the Massachusetts Institute of Technology. “I’d say that the vintage of more than a million years, which is the age of HD 100453, is quite a good one.”
What made this discovery possible? Because HD 100453 has a higher mass than the Sun, it has a warmer, planet-forming disk around it. This causes molecules in the disk, including methanol, to exist as gas at larger distances from the star, enabling ALMA to detect it. By contrast, less massive stars like the Sun have cooler disks so methanol would be locked up in ice and ALMA cannot detect it.
The ratio of methanol to other simple organic molecules seen in HD 100453 is about the same as it is in comets in our Solar System. This reinforces the potential to learn about our own planet’s history by studying these more distant early worlds.
More specifically, this work suggests that the ices within planet-forming disks, which serve as the material that will eventually clump together to form comets, are rich in complex organic molecules.
“This research supports the idea that comets may have played a big role in delivering important organic material to the Earth billions of years ago,” said co-author Milou Temmink of Leiden Observatory in the Netherlands. “They may be the reason why life, including us, was able to form here.”
Methanol had previously been detected in several star-forming disks, but detecting isotopes of methanol — which are 10 to 100 times less abundant — is an important step because it confirms that the disks are likely rich in organic molecules not yet detected in HD 100453, including simple amino acids and sugars such as glycine and glycolaldehyde.
High levels of methanol in the disk likely come from the inner edge of a ring of dust about 1.5 billion miles from the star, equivalent to 16 times the distance between the Sun and the Earth.
A paper describing these results appears in The Astrophysical Journal.
Astrobiolgy, Astrochemistry,
