When it comes to the universe and all of its mysteries, there are many things we know we don't know. Some are minor and mostly inconsequential, but there are other cosmological unknowns that leave huge blanks in our understanding of how things work on large and small scales. How our planet was created is one such mystery. Let's go all the way back to the beginning when the Sun was just a clump of gas and dust to understand how our solar system may have formed.
How stars form
Traditional wisdom says that all stars spawn from immense clouds of spinning gas and dust, known as molecular clouds, often containing the mass of hundreds of millions of stars. The environment within these stellar nurseries tends to be extremely turbulent, preventing all of the gas and dust from being distributed evenly throughout the molecular cloud. Drawn together by the forces of gravity, once enough matter has collected in one area, the cloud begins to heat up and ultimately collapses under its own weight -- creating something known as a protostar. Feeding off the material encircling it, the protostar eventually becomes hot and large enough to jumpstart the process of thermonuclear fusion.
"Young protostars put on weight by gathering matter from a dense disk of gas and dust that swirls around them. But once protostars grow beyond a certain size, further accretion is hampered by the light they emit. This may happen when ultraviolet light strips electrons from atoms in the surrounding disk to produce a hot ionized plasma that evaporates from the star, a process called photoevaporative outflow," Riken reports.
"Theoretical calculations have suggested that this and related factors are too weak to stop accretion. But there is insufficient observational evidence to back this up, not least because the most massive protostars are rare and very distant from the Earth."
Now, in a new paper, recently published in Nature Astronomy, researchers have made a discovery that could help shed light on the earliest days of our solar system, from the formation of the Sun to the birth of planets, and ultimately why Earth is the way it is -- formed in just the right place and time to make it habitable.
Introducing IRS 63
IRS 63 is a protostar located about 470 light-years from Earth in the constellation of Ophiuchus. It's estimated to be merely half a million years or so in age, but it just so happens to be one of the youngest and brightest protostars for its age in what is essentially our stellar neighborhood.
The protostar is encompassed by a huge cloud of gas and dust that is larger than most stars its age. The disk is about 50 AU's in size. For context, one astronomical unit is the average distance between our planet and the Sun, one unit is 93 million miles (150 million kilometers).
"The size of the disk is very similar to our own solar system, Even the mass of the protostar is just a little less than our sun's," the leader of a study on IRS 63 -- an astronomer who hails from the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, Dominique Segura-Cox said.
The team decided to point the Atacama Large Millimeter/sub-millimetre Array (ALMA), known as one of the sharpest and most powerful telescopes for studying radio waves, at the object and they discovered that it has gaps and rings within the disk, which is indicative of planet formation. One of the gaps, the innermost one, is located about 19 astronomical units from the center of the disk and is estimated to be 3.2 AUs wide. The outermost gap is a little larger. Located 37 AU from the protostar's core, it is 4.5 AUs wide.
The rings are very bright. One is 27 AU from the protostar's core and is 6 AUs in size. The other is 51 AUs from the center of the blooming star, and is estimated to be about 13 AUs in width. Our models of how stars eventually create planets say that planets form in a similar way to stars. Gravity brings clumps of gas and dust together, siphoning gas and dust from elements that fused together as the protostar produced heavier and heavier elements.
Naturally, it makes sense that the gaps in the debris disks could be the result of gravity pulling gas and dust together, carving out spaces as the matter slowly collects and becomes protoplanets. Should that be the case for IRS 63, astronomers believe the innermost gap may be due to the formation of a planet with about half of Jupiter's mass.
"The rings in the disk of IRS 63 are so young. We used to think that stars entered adulthood first and were the mothers of planets that came later, but now we see that protostars and planets grow and evolve together from early times, like siblings," says Segura-Cox.
"The rings in the disk of IRS 63 are vast pile-ups of dust, ready to combine into planets. However, even after the dust clumps together to form a planet embryo, the still-forming planet could disappear by spiraling inwards and being consumed by the central protostar. If planets do start to form very early and at large distances from the protostar, they may better survive this process,” Dr. Anika Schmiedeke, also from the Max Planck Institute for Extraterrestrial Physics added.
What does this mean for our solar system?
Equipped with the knowledge that planets and stars might grow alongside one another, this research has significant implications for our understanding of how our solar system came to be.
Within the disk of IRS 63 lies approximately 150 Earth masses of material. Additionally, It is believed that it requires 10 Earth masses of material at minimum in order for a protoplanet to start gathering enough gas and dust to inevitably form a gas giant. Yichen Zhang of the RIKEN Star and Planet Formation Laboratory studied another protostar that gave us a glimpse at how protoplanets grow large enough to become gas giants, and it's a little bit more complicated than we once thought.
According to RIKEN, "Their observations showed that the gas reaches temperatures of about 10,000 degrees Celsius and moves at about 30 kilometers per second. This suggests that the hourglass-shaped region is filled with ionized gas that has been launched away from the protostar’s disk by light-driven ionization."
As for IRS 63, “These rings and gaps suggest that we are seeing the earliest evidence of planet formation, and that planets certainly start to form within the first half million years, and probably within the first 150,000 years, Planets, especially planets like Jupiter, started their own formation at one of the earliest stages of the star formation process," says Ian Stephens, an astronomer from the Center for Astrophysics, Harvard & Smithsonian (CfA)
"Astronomical observations reveal that protoplanetary disks around young stars commonly have ring- and gap-like structures in their dust distributions. These features are associated with pressure bumps trapping dust particles at specific locations, which simulations show are ideal sites for planetesimal formation. Here we show that our Solar System may have formed from rings of planetesimals—created by pressure bumps—rather than a continuous disk," the Nature Astronomy paper further notes.
We still have a way to go before we have a complete understanding of how Earth-like planets and gas-giants form, but these pieces of research have helped tremendously. We need to study more protoplanets in the midst of formation.