Over the past 30 years, astronomers have
found more than 5,000
exoplanets, an eclectic menagerie of worlds far from our
stellar neighborhood. The latest may be a mere infant.
اضافة اعلان
In the journal The
Astrophysical Journal Letters,
scientists on Tuesday announced compelling evidence for a world just 1.5
million years old, making it one of the youngest planets ever found, perhaps
the youngest.
This world — 395 light-years from
Earth in the
constellation Ophiuchus — is so young that its building blocks of gas and dust
are still coming together. This planet is a newborn being cradled in the arms
of its parent star.
“It is like looking at our own past,” said Myriam
Benisty, an astronomer at the Institute of Planetology and Astrophysics of
Grenoble in France and a co-author of the study.
As the suspected planet is shrouded by the matter
that is making it, further telescopic observations will be required to confirm
its existence. Presuming it is not rocky detritus masquerading as a planet,
scientists can use it to better understand how worlds are made.
The torrent of newly discovered exoplanets has
complicated or disproved long-standing theories of planet formation. But the
location of this baby planet — firmly within the disk of primordial matter
around its star — supports the idea that most planets spend much of their time
growing up in a similar sort of nursery.
The discovery of the celestial pip suggests “all
planetary systems have a common formation process,” said Anders Johansen, an
astronomer at Lund University in Sweden who was not involved with the study.
Despite the chaos of the cosmos, he said, “there is actually a lot of order”
when it comes to crafting planets.
The team of scientists used the Atacama Large
Millimeter/submillimeter Array (ALMA), a collection of 66 antennas acting in
unison in Chile, to gather evidence of this exceedingly young world. Gas and
dust orbits certain stars in so-called circumstellar disks. This material,
which clumps together to form planets within these disks, emits radio waves
that ALMA can detect.
Last year, Benisty and her colleagues used ALMA to
make the first unambiguous detection of a halo of gas and dust orbiting an
exoplanet: a circumplanetary foundry still making the world it shrouded, and
perhaps a few moons, too.
For the latest study, they pointed ALMA at AS 209, a
star just a tad heavier than the sun. Just 1.5 million years of age, it has
only recently started to burn hydrogen — the stellar equivalent of a toddler
uttering its first words.
AS 209’s circumstellar disk was found to have
several gaps. And in one such gap, ALMA detected the radio-wave signature of a
planet-making tempest, gas that was presumably enveloping a Jupiter-like world
still under construction.
The planet’s precise age will not be resolved soon,
but it’s likely to be very similar to its nascent star. But its youth is not
the only thing piquing astronomers’ interests. It is also bafflingly far from
its star. Neptune, the outermost planet in our solar system, is roughly 2.8
billion miles from the sun. This exoplanet is almost 19 billion miles away from
its own star.
That raises questions about our own neck of the
woods.
The size of the debris disk that forged Earth and
the other planets is uncertain. “Maybe the disc was only slightly larger than
Neptune’s orbit, and that is why Neptune is the outermost planet,” Johansen
said. But perhaps our hub of planet-making matter was more like AS 209’s. If
so, “we also cannot rule out that our own solar system has a planet beyond
Neptune,” he said — perhaps the hypothesized Planet 9 that some astronomers
suspect is lingering in distant darkness.
In the coming days, the
James Webb Space Telescope
will determine the mass of the planetary newborn and study its atmospheric
chemistry. And by painting a detailed portrait of one of the youngest worlds
known to science, these observations will inch us all closer to answering the
ultimate question, said Jaehan Bae, an astronomer at the University of Florida
and an author of the study: “Where did we come from?”
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