Podcaster: Richard Drumm
Title: UNAWE Space Scoop – When Stars Wobble
Organization: 365 Days Of Astronomy
Description: Space scoop, news for children.
Using the VLBA, the National Science Foundation’s Very Long Baseline Array of radio telescopes, astronomers have found a Saturn-sized planet orbiting a small, cool star that’s only 35 light years away! It’s called TVLM 513–46546, it’s in the direction of the constellation Boötes and it’s right in our neighborhood! The planet has about a third of Jupiter’s mass and is closer to its star than Mercury is to our Sun and it orbits its star once every 221 days.
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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This is the 365 Days of Astronomy Podcast. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Today’s story is…
When Stars Wobble
Although there are many planets in the Universe of various sizes, colors and characteristics, some are particularly unusual or unique!
New observations from the National Science Foundation’s NOIRLab and other telescopes have found a planet that doesn’t quite match how astronomers expected planets to form.
In 2016, astronomers found a young exoplanet known as K2-25b. This planet is orbiting a young M 4.5 red dwarf star, K2-25, in the Hyades star cluster in the constellation Taurus.
The, uh, “young” system is 600 to 800 million years old, just a baby, and is located about 150 light years away from Earth.
The astronomers used a variety of telescopes in the research. One of the major instruments was the HPF, the Habitable-zone Planet Finder spectroscope attached to the 10 meter Hobby-Eberly Telescope at the McDonald Observatory in Texas.
This instrument provided the radial velocity measurements of the star’s motion as it’s orbited by the planet. It also provided clear evidence for starspots, like our Sun’s sunspots, on the parent star.
Data from the NASA Kepler K2 mission was also used as this is a transiting exoplanet where the planet passes in front of the star, dimming the star’s light a tiny bit.
They also used the Engineered Diffuser on the ARCTIC imager of the 3.5 meter telescope at the Apache Point Observatory, and the HDI, the Half Degree Imager on the popular .9 meter WIYN telescope, built in 1960, at Kitt Peak Observatory.
By the way, WIYN stands for Wisconsin, Indiana, Yale & NOAO, the founding members of the consortium who footed the original 1994 construction costs of the 3.5 meter WIYN telescope.
Yale has withdrawn from the consortium and has been replaced by the University of Missouri, and NASA & the NSF have taken over the NOAO share of the costs.
Now where was I? Oh yeah!
K2-25b orbits an M dwarf star. This is the most common type of star in the galaxy.
What makes this planet peculiar is that it’s unusually dense for its size and its young age.
K2-25b weighs 20 to 30 times Earth’s mass and is about 3 1/2 times the radius of Earth. So it’s slightly smaller than the planet Neptune, but almost 50% more massive than Neptune!
It appears to have a thin hydrogen & helium atmosphere, that accounts for 5% of the planet’s mass, sitting on a rocky core that accounts for the rest.
Using the RM or Rossiter-McLaughlin Effect, the astronomers were able to approximately measure the obliquity of this planet’s rotation about its axis and found it to be low, with the measurement centered on 3°.
Earth is tilted over at about 23 1/2° from it’s path about the Sun, which gives us seasons, so we have a fairly normal obliquity.
Only 4 exoplanets orbiting M dwarfs have had their obliquities measured, because the exoplanets are so darned faint.
Perhaps the new crop of super-sized telescopes will pull in enough photons of exoplanet light to make the measurements needed to study this phenomenon.
All this presented a mismatch between this exoplanet and how astronomers understood planets to form. Big rocky cores form and then they have gravity enough to pull in gasses till they resemble Neptune or Jupiter.
But K2-25b has the big core without the huge atmosphere.
Planets of this size are usually made mostly of gas and are known as gas giants like Jupiter and Saturn, or ice giants like Uranus and Neptune.
However, K2-25b is made almost entirely of rock! This is why the planet is so very dense, but it’s also a big mystery.
Planets with sizes between those of Earth and Neptune are common throughout our galaxy. These are called “sub-Neptune” planets and we obviously don’t have any in our own Solar System.
Uranus is slightly larger than Neptune, but has slightly less mass. So our Ice Giants are more or less twins.
How this type of planet forms and evolves is an area of particular interest and curiosity for planetary astronomers. Planets are expected to form on nice, simple, circular, coplanar orbits in their protoplanetary disks.
But maybe they form in a more complicated way!
Astronomers will continue to study this mysterious planet in hopes of figuring out the mystery as to how and why it formed like it did.
Hey Here’s A Cool Fact:
One year on planet K2-25b passes very quickly. This planet orbits its star in only 3 1/2 Earth days!
I don’t EVEN want to know how many years old I’d be over there!
Thank you for listening to the 365 Days of Astronomy Podcast!
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365 Days of Astronomy
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