Scientists have discovered that a distant “hot Jupiter” has a planetary companion. The two planets perform a rhythmic dance around the star TOI-1408, 455 light-years away from Earth. TOI-1408 b was discovered last year by NASA’s Transiting Exoplanet Survey Satellite (TESS). It is a gas giant that is more than twice the width of Jupiter and almost twice as massive as any gas giant in the solar system. It orbits its parent star at a distance of 8.5 million kilometers, which is about 6% of the distance between Earth and the Sun.
This means that TOI-1408 b completes an orbit in just 4.4 Earth days. Due to its size and closeness to its star, TOI-1408 b is classified as a “hot Jupiter,” but what’s notable is that the newly discovered companion star is even closer to the system’s primary star. Companion star TOI-1408 c is just 3.3 million miles from its star, which means it completes an orbit in 2.2 Earth days. Still, this newly discovered planet is not a hot Jupiter. Roughly twice the width of Earth and eight times its mass, TOI-1408 c is classified as a “super-Earth” or “sub-Neptune.”
Unlike TOI-1408 b, which is mostly gas, TOI-1408 c is likely composed of a mixture of gas and rock. “Both TOI-1408 b and TOI-1408 c are incredibly close to their parent stars compared to planets in our solar system,” lead study author Judith Kors of Lund University told Space.com. “Imagine our solar system, but instead we have Jupiter revolving around the Sun roughly every four days, which is 1/20th of the revolution of Mercury. “It’s already very close to the star, but now we’ve discovered another planet even closer to it, which is interacting strongly with its larger neighbor, causing fluctuations in its orbit that we’ve never seen before.”
“The discovery of a hot Jupiter with a perturbed orbit like TOI-1408 b is intriguing because it’s unusual for such a massive planet. But the discovery that there’s an even smaller planet moving the larger one in its orbit was even more unexpected,” she continued. “This discovery calls into question some of our assumptions about the formation of these planetary systems, because we don’t usually think about the discovery of a smaller planet, a low-mass planet in the orbit of a hot Jupiter. ” But there’s something else that makes this system extraordinary: the finely tuned rhythmic dance that its two planets perform.
This is despite the smaller TOI-1408c tugging at its dance partner, a hot Jupiter, and the TOI-1408 system appears to have a stable configuration that allows these two planets to coexist in close orbits. “Probably as a result of its evolutionary history, the dynamics of the system are finely tuned. The planets’ orbital periods are roughly 2:1, meaning that for every orbit of TOI-1408c, TOI-1408b orbits the star once,” said Course. “This could help stabilize their orbits despite their close proximity to each other and to the star.”
She added that the exact reason the TOI-1408 system formed this way is probably because the planets migrated through a disk of gas and dust that surrounded its star in its early days, a so-called “protoplanetary disk.” was formed. TESS has discovered more than 7,000 possible exoplanets since its launch in 2018, making it an extraordinary exoplanet hunter. The TOI 1408 planets are the two youngest. NASA’s exoplanet hunters surveyed 200,000 of the brightest stars near the Sun to find planets that cross, or “transit,” the face of their parent stars, creating small dips in the star’s light. A star called TOI-1408 is just such a star. TOI-1408 is 1.3 times the mass of the Sun and 1.5 times the width of its star, and is slightly hotter and more luminous than the Sun.
TESS discovered both TOI-1408 b and TOI-1408 c, but the smaller planet was a bit harder to detect. “TOI-1408 c was more difficult to detect because its transit was much shallower as it passed in front of the star from our perspective, blocking less light from the star compared to TOI-1408 b,” Course said. “Furthermore, the transit of TOI-1408 c is subject to significant transit time variations (TTV), meaning that the timing of its transits is not as predictable as TOI-1408 b.”
The research team found a transit signal that could have come from another small planet with a shorter orbital period than the known planet, and used photodynamic modeling, which combines and calculates both the transit light curve and radial velocity data, to further characterize the nature of the asteroid candidate. Complex interactions between the planets must be taken into account. The team has not yet completed development of the TOI-1408 system, but there are indications that at least three worlds may exist. However, if there are more planets in the system, it is unlikely that they will be within the orbit of TOI-1408 c.
“There are indications that there may be a third planet in this system that is more distant. This is based on radial velocity data that shows a possible long-term trend. But we still do not have evidence for a planet even closer than TOI 1408 c was found,” said Course. “TOI-1408 c is already so close to the star that it would be difficult for any other planet to maintain a stable orbit within it.” NASA’s exoplanet hunters surveyed 200,000 of the brightest stars near the Sun to find planets that cross, or “transit,” the face of their parent stars, causing a slight dip in the star’s light.
A star called TOI-1408 is just such a star. TOI-1408 is 1.3 times the mass of the Sun, 1.5 times the width of its star, and slightly hotter and more luminous than the Sun. TESS found both TOI-1408 b and TOI-1408 c, but the smaller planet was slightly harder to detect.
source: https://arxiv.org/abs/2407.17798