Surprisingly dense exoplanet challenges planet formation theories

Surprisingly dense exoplanet challenges planet formation theories

New detailed observations with NSF’s NOIRLab amenities reveal a younger exoplanet, orbiting a younger star within the Hyades cluster, that’s unusually dense for its dimension and age. Weighing in at 25 Earth-masses, and barely smaller than Neptune, this exoplanet’s existence is at odds with the predictions of main planet formation theories.

Surprisingly dense exoplanet challenges planet formation theories
New detailed observations with NSF’s NOIRLab amenities reveal a younger exoplanet, orbiting a younger star within the Hyades
cluster, that’s unusually dense for its dimension and age. Barely smaller than Neptune, K2-25b orbits an M-dwarf star
– the commonest sort of star within the galaxy – in 3.5 days [Credit: NOIRLab/NSF/AURA/J. Pollard]

New observations of the exoplanet, often known as K2-25b, made with the WIYN 0.9-meter Telescope at Kitt Peak Nationwide Observatory (KPNO), a Program of NSF’s NOIRLab, the Pastime-Eberly Telescope at McDonald Observatory and different amenities, increase new questions on present theories of planet formation. The exoplanet has been discovered to be unusually dense for its dimension and age—elevating the query of the way it got here to exist. Particulars of the findings seem in The Astronomical Journal.

Barely smaller than Neptune, K2-25b orbits an M-dwarf star—the commonest sort of star within the galaxy—in 3.5 days. The planetary system is a member of the Hyades star cluster, a close-by cluster of younger stars within the route of the constellation Taurus. The system is roughly 600 million years previous, and is positioned about 150 light-years from Earth.

Planets with sizes between these of Earth and Neptune are widespread companions to stars within the Milky Approach, even if no such planets are present in our Photo voltaic System. Understanding how these “sub-Neptune” planets type and evolve is a frontier query in research of exoplanets.

Astronomers predict that big planets type by first assembling a modest rock-ice core of 5-10 occasions the mass of Earth after which enrobing themselves in an enormous gaseous envelope lots of of occasions the mass of Earth. The result’s a gasoline big like Jupiter. K2-25b breaks all the principles of this typical image: With a mass 25 occasions that of Earth and modest in dimension, K2-25b is sort of all core and little or no gaseous envelope. These unusual properties pose two puzzles for astronomers. First, how did K2-25b assemble such a big core, many occasions the 5-10 Earth-mass restrict predicted by principle? And second, with its excessive core mass—and consequent sturdy gravitational pull—how did it keep away from accumulating a major gaseous envelope?

Surprisingly dense exoplanet challenges planet formation theories
An instance of a 5 cm by 5 cm (2 inch by 2 inch) Engineered Diffuser
[Credit: Gudmundur Stefansson/RPC Photonics]

The group finding out K2-25b discovered the outcome stunning. “K2-25b is uncommon,” stated Gudmundur Stefansson, a postdoctoral fellow at Princeton College, who led the analysis group. Based on Stefansson, the exoplanet is smaller in dimension than Neptune however about 1.5 occasions extra huge. “The planet is dense for its dimension and age, in distinction to different younger, sub-Neptune-sized planets that orbit near their host star,” stated Stefansson. “Normally these worlds are noticed to have low densities—and a few even have prolonged evaporating atmospheres. K2-25b, with the measurements in hand, appears to have a dense core, both rocky or water-rich, with a skinny envelope.”

To discover the character and origin of K2-25b, astronomers decided its mass and density. Though the exoplanet’s dimension was initially measured with NASA’s Kepler satellite tv for pc, the scale measurement was refined utilizing high-precision measurements from the WIYN 0.9-meter Telescope at KPNO and the three.5-meter telescope at Apache Level Observatory (APO) in New Mexico. The observations made with these two telescopes took benefit of a easy however efficient approach that was developed as a part of Stefansson’s doctoral thesis.

The approach makes use of a intelligent optical element referred to as an Engineered Diffuser, which might be obtained off the shelf for round $500. It spreads out the sunshine from the star to cowl extra pixels on the digital camera, permitting the brightness of the star in the course of the planet’s transit to be extra precisely measured, and leading to a higher-precision measurement of the scale of the orbiting planet, amongst different parameters.

“The modern diffuser allowed us to raised outline the form of the transit and thereby additional constrain the scale, density and composition of the planet,” stated Jayadev Rajagopal, an astronomer at NOIRLab who was additionally concerned within the research.

Surprisingly dense exoplanet challenges planet formation theories
Sundown on the WIYN 0.9 Meter Telescope at Kitt Peak Nationwide Observatory
[Credit: KPNO/NOIRLab/NSF/AURA/P. Marenfeld]

For its low value, the diffuser delivers an outsized scientific return. “Smaller aperture telescopes, when outfitted with state-of-the-art, however cheap, tools might be platforms for prime affect science packages,” explains Rajagopal. “Very correct photometry might be in demand for exploring host stars and planets in tandem with house missions and bigger apertures from the bottom, and that is an illustration of the function {that a} modest-sized 0.9-meter telescope can play in that effort.”

Due to the observations with the diffusers out there on the WIYN 0.9-meter and APO 3.5-meter telescopes, astronomers at the moment are capable of predict with larger precision when K2-25b will transit its host star. Whereas earlier than transits might solely be predicted with a timing precision of 30-40 minutes, they’re now recognized with a precision of 20 seconds. The advance is crucial to planning follow-up observations with amenities such because the worldwide Gemini Observatory and the James Webb Area Telescope.

Most of the authors of this research are additionally concerned in one other exoplanet-hunting challenge at KPNO: the NEID spectrometer on the WIYN 3.5-meter Telescope. NEID allows astronomers to measure the movement of close by stars with excessive precision—roughly 3 times higher than the earlier technology of state-of-the-art devices—permitting them to detect, decide the mass of, and characterize exoplanets as small as Earth.

Supply: Affiliation of Universities for Analysis in Astronomy (AURA) [August 04, 2020]

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