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In our solar system, the planetary orbits all have a similar orientation. Their orbital planes vary by a few degrees, but roughly the planets all orbit in the same direction. This invariable plane as it’s known also has an orientation within a few degrees of the Sun’s rotational plane. Most planetary systems have a similar arrangement, where planetary orbits and stellar rotation are roughly aligned, but a few exoplanets defy this trend, and we aren’t entirely sure why.

Common orientation within a planetary system makes sense given how planetary systems form. The protostellar cloud out of which a star and its planets form usually has some inherent rotational momentum. As a star begins to coalesce, a protoplanetary disk forms around the star. Since the planets form within this disk, they all end up with similar orbits. Things can be more complicated with binary or multiple-star systems, but you’d expect single-star planetary systems to have an invariable plane similar to ours. However, this isn’t true for a planetary system known as WASP-131, as a recent study shows.

WASP-131 is known to have at least one planet, 131b. It’s a hot gas planet with a mass a bit less than Saturn that orbits 131 every five days. Earlier studies of 131b found the planet unusual because of how thick its atmosphere is. Although its mass is only a quarter that of Jupiter, its diameter is 20% larger than Jupiter’s. 131b has such a low density for a gas planet that it’s known as a super-puff planet.

The planet was discovered via the transit method, which means it passes in front of its star from our point of view. It’s an effective way to find exoplanets, but it can also be used to verify the rotational motion of the star. Because of stellar rotation, light coming from the region of the star rotating toward us is slightly blueshifted, and light from the region rotating away from us is slightly redshifted. This means that spectral lines from the star are blurred a bit. The effect is known as Doppler broadening. As the planet passes in front of the star, it blocks a part of the blueshifted and redshifted regions in turn. This causes the spectral lines of the star to shift a bit. This Rossiter–McLaughlin effect as it’s known allows astronomers to measure the orientation of stellar rotation.

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An illustration of the Rossiter–McLaughlin effect. Credit: Wikipedia user Autiwa

When the team analyzed the rotation of WASP-131, they found it wasn’t similar to that of its planet. The orbit of 131b is tilted about 160 degrees from the rotational plane of the star, meaning that it is in a high, almost polar retrograde orbit. Of course, this raises the question of just how the planet could have gotten such an odd orbit.

One idea is a process known as the Kozai effect. Dynamical interactions between the planet, its star, and other planets in the system can cause the orbit to shift away from the invariant planet. We see this in our own solar system with Pluto and Neptune, which has tilted Pluto’s orbit over time. The Kozai effect is more pronounced with smaller planets, however, and interaction between planet and star alone isn’t enough to explain such an inclined orbit. Another possibility is a magnetic interaction between the planet and the protoplanetary disk early in its formation period.

Although the mechanism behind the odd orbit isn’t clear, it does follow a pattern seen with many hot gas exoplanets. About a quarter of them have significantly tilted orbits. It seems that these planets sometimes get way out of line.

Reference: Doyle, L., et al. “WASP-131 b with ESPRESSO I: A bloated sub-Saturn on a polar orbit around a differentially rotating solar-type star.” arXiv preprint arXiv:2304.12163 (2023).

The post Bizarre Exoplanet Breaks All the Orbital Rules appeared first on Universe Today.

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Transporter-8 Mission

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June 10, 2023

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SpaceX is targeting Monday, June 12 for Falcon 9’s launch of the Transporter-8 mission to low-Earth orbit from Space Launch Complex 4E (SLC-4E) at Vandenberg Space Force Base in California. The 57-minute launch window opens at 2:19 p.m. PT (21:19 UTC). If needed, there is a backup opportunity Tuesday, June 13 with the same window.

The first stage booster supporting this mission previously launched NROL-87, NROL-85, SARah-1, SWOT, and four Starlink missions. Following stage separation, Falcon 9 will land on Landing Zone 4 (LZ-4) at Vandenberg Space Force Base.

Transporter-8 is SpaceX’s eighth dedicated smallsat rideshare mission. There will be 72 payloads on this flight, including CubeSats, MicroSats, a re-entry capsule, and orbital transfer vehicles carrying spacecraft to be deployed at a later time.

A live webcast of this mission will begin about 15 minutes prior to liftoff.

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Triggered Star Birth in the Nessie Nebula

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June 9, 2023

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Star formation is one of the oldest processes in the Universe. In the Milky Way and most other galaxies, it unfolds in cold, dark creches of gas and dust. Astronomers study sites of star formation to understand the process. Even though they know much about it, some aspects remain mysterious. That’s particularly true for the “Nessie Nebula” in the constellation Vulpecula. An international team led by astronomer James Jackson studies the nebula and its embedded star-birth regions. They found that it experienced a domino effect called “triggered star formation.”

“So, one of the interesting and open questions remaining in the field of star formation is, what happens when a star forms and ejects energy into the surrounding medium?” he said. “Does it make new stars, or does it prevent the formation of new stars?”

To answer those questions, Jackson and an international team of observers peered deep into the Nessie Nebula. It’s a so-called “Infrared Dark Cloud” (IRDC) with the official catalog name Lynds 772. Jackson named it the Loch Ness Monster Nebula a few years back. That’s because it resembles a spindly version of the famous and elusive Scottish lake monster. What the team found reveals that triggered star formation actually does take place under special circumstances in this nebula.

Putting the Nessie Nebula in Perspective

In 2013, Dr. Alyssa Goodman of Harvard Center for Astrophysics called the Nessie Nebula one of the “bones” of the Milky Way. That’s because it’s one of many webs of dusty filaments threaded through the galaxy. “It’s possible that the Nessie bone lies within a spiral arm, or that it is part of a web connecting bolder spiral features,” she said, noting that it probably spans at least 80 parsecs long and about a half-parsec wide.

As a galactic “bone”, it’s a prime place to look for triggered star formation. Nessie has a density of about 600 solar masses per parsec across its entire length. It’s also cold, with an average temperature of about 10K. There are many such cold clouds in the Milky Way, notably places like the famous Pillars of Creation or regions in the Carina Nebula.

The Pillars of Creation is another region of cold, dark gas similar to the Nessie Nebula where young stars are forming. Image Credit: NASA/ESA/CSA
The Pillars of Creation is similar to the Nessie Nebula where young stars are forming. Image Credit: NASA/ESA/CSA

A star gets started when gravity pushes the material in the cloud together to form a hot core. Temperatures and pressures rise, and eventually, a star is born. The Nessie Nebula is actually dense enough to form many very high-mass stars, according to Jackson. “By high mass, I mean a star that’s about 8 times the mass of the Sun, or more,” he said. “They have so much more energy than the Sun, and they inject this energy into the surrounding material, and they form these H II bubbles that ionize the gas around them.”

Essentially, those H II bubbles form as stellar winds from the hot young protostars push into surrounding space and photoionize (or heat) the gas there. As they expand, they stir up material around them. That creates a lot of energy. “The question I’m trying to answer is, does this energetic feedback trigger or hinder the formation of other new stars?” said Jackson.

The Domino Effect in the Nessie Nebula

The scenario for triggered star formation requires an almost perfect set of circumstances, starting with the cold dense nebula. Jackson explained that once a star (or group of stars) forms, its H II bubble triggers the birth process of the next star. That process repeats, almost like a domino effect.

So, does this triggered star formation really happen? Jackson pointed out two different scenarios. “If bubbles are just dispersing the gas, then that gas is gone and no stars can form,” he said. “On the other hand, if you have a clump of gas that’s almost ready to make a star, but not quite, can you hit it with an expanding shell and compress it? It could push it over the edge and gravity can take over. Some people say you make new stars and some say you don’t.”

To find out, the team looked at Nessie with the infrared-sensitive SOFIA flying observatory. It allowed them to peer through the clouds of gas and dust at the central region of the nebula. They coupled their observations with radio data from the Australia Telescope Compact Array and the Mopra radio dish. They zeroed in on its most luminous young stellar object, called AGAL337.916-00.477. This high-mass stellar object is part of a cloud in the nebula that has several other high-mass young stellar objects and so-called “dust cores” where the process of star

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New Detailed Images of the Sun from the World’s Most Powerful Ground-Based Solar Telescope

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June 9, 2023

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Our Sun continues to demonstrate its awesome power in a breathtaking collection of recent images taken by the U.S. National Science Foundation’s (NSF’s) Daniel Inouye Solar Telescope, aka Inouye Solar Telescope, which is the world’s largest and most powerful ground-based solar telescope. These images, taken by one of Inouye’s first-generation instruments, the Visible-Broadband Imager (VBI), show our Sun in incredible, up-close detail.

“These images preview the exciting science underway at the Inouye Solar Telescope,” Dr. Alexandra Tritschler, who is a National Solar Observatory Senior Scientist, tells Universe Today. “These images are a small fraction of the data obtained from the first Cycle. They exemplify the many and much broader science objectives and the much more powerful spectroscopy and spectropolarimetry data that now goes along with the images, none of which was available in 2020 when the Inouye Solar Telescope released its first-light images.”

The solar features in Inouye’s images include sunspots which reside in the Sun’s photosphere. These are the dark spots on the Sun’s “surface” and one of the Sun’s most well-known features, often reaching sizes that equal, or even dwarf, the size of the Earth. It is their dark appearance that can be deceiving, however, as sunspots are responsible for solar flares and coronal mass ejections that produce solar storms, which is a type of space weather.

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Image of a sunspot taken by the Inouye Solar Telescope. While they have a dark appearance, sunspots are responsible for solar flares and coronal mass ejections that produce solar storms. Sunspots often reach sizes that equal, or even dwarf, the size of the Earth. (Credit: National Science Foundation (NSF)/Association of Universities for Research in Astronomy, Inc. (AURA)/National Solar Observatory (NSO))
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Image of a sunspot with a light bridge, which is hypothesized to be the beginning stages of a degrading sunspot. (Credit: NSF/AURA/NSO)

Other features from the Inouye images include convection cells, which also reside in the Sun’s photosphere, and consist of upward- and downward-flowing plasma, known as granules or “bubbles”. The last feature in the Inouye images are fibrils, which exist in the Sun’s chromosphere and are produced from the magnetic field interactions within the Sun.

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Image of solar granules or “bubbles”, intergranular lanes, and magnetic elements in the quiet regions of the Sun. In these features, solar plasma rises in the
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