In our Solar System, the giant planets are the outer four of the eight planets, Jupiter, Saturn, Uranus, and Neptune. In other words, they are the Jovian planets. However, these planets are split into two categories of giant planets: gas giant and ice giant. While all four of the planets are gaseous in their composition, Jupiter and Saturn are the only ones considered gas giants. This is due to the fact that Uranus and Neptune differ slightly in composition. In the case of “traditional” giant planets, such as Jupiter and Saturn, their mass is mostly made up of hydrogen and helium. However, Uranus and Neptune are instead mostly composed of water, ammonia, and methane, leading to their title as “ice giants. Giant planets lack surfaces given their gaseous nature, therefore, landing on a giant planet may not be possible, depending on the size and composition of its core.
Pluto was once the 9th planet of our Solar System. However, it has since been rebranded as a “dwarf planet.” Pluto is located in a distant region of the Solar System called the Kuiper Belt, found beyond the location of Neptune. Pluto was discovered in 1930 by an astronomer named Clyde Tombaugh and named by an 11 year old from Oxford, England. As for the planet itself, it has an equatorial diameter of 1,477 miles and is about 39 times farther from the Sun than the Earth. Pluto’s orbit is slightly unusual when compared to the other planets as it’s elliptical and tilted. It takes Pluto 248 years to orbit the Sun once and one day on Pluto lasts for 153 hours. Its axis of rotation is tilted at 57 degrees, making Pluto spin almost on its side. Finally, Pluto has five known moons: Charon, Nix, Hydra, Kerberos, and Styx.
Extrasolar planets, or as they are better known: exoplanets, refers to any planet that exists outside of our own solar system, which is quite a lot. Astronomers are naturally very interested in planets in other solar systems, learning about their properties, sizes, or age. This information helps us understand our own solar system but also is critical for one of the most hopeful parts of astronomy: space exploration. Something that we are looking for is planets that are most similar to Earth, partially to see if there is another planet that we could inhabit if we ever need to do, but also because it would strongly indicate the presence of alien life.
One of the exoplanets we currently know of is Kepler-452b, it is relatively similar to Earth in size, orbits a similar class star, and is in the habitable zone. It is not unlikely that life is present there, or on some other exoplanet.
Not all exoplanets are like Earth however, in fact most of them are very different. Take a look at WASP-103b, which is the first non spherical planet discovered, its more of a football shape. On HD-189733b, instead of water, it rains molten glass. Every planet has its own unique properties and the more we find, the more incredible things we learn.
Considering that we have found around 5,600 total exoplanets so far, out of the billions or more that actually exist, there is still much more to discover.
The Kuiper Belt is a very important region of our solar system, and objects in the Kuiper Belt have been essential in helping scientists determine how the solar system formed. Most of these objects are small and icy, with some (relatively) large enough to be accepted as dwarf planets, such as Pluto.
In this blog post I wanted to explore how scientists have managed to study the Kuiper Belt from billions of miles away. Pluto was first discovered in 1930 but it wasn’t until many years later that scientists found evidence for the Kuiper Belt. In 1987, David Jewitt and his graduate student Jane Luu began searching for other objects beyond Pluto’s orbit, and in 1992 announced their discovery of the icy object “15760 Albion”. 6 months later, they also announced the discovery of a second object, “1993 FW”.
We have since discovered thousands of objects in the Kuiper Belt, with thousands more theorized to exist. However, all of these objects had only been observed from the Earth using telescopes. That is until 2015, when the spacecraft New Horizons flew by Pluto and began to investigate further objects in the Kuiper Belt. Observations from the Hubble space telescope were used to identify target objects, and one was selected for New Horizons to fly by. In 2019, New Horizons successfully flew by this target, named 486958 Arrokoth, and revealed that it was a “contact binary” formed from two planetesimals slowly joining together. This is the farthest object in our solar system ever visited by a spacecraft, and the pictures from the flyby are amazing to see.
The Grand Tack hypothesis theorizes that Jupiter formed much farther out from the sun than it currently is, migrated inwards quite a bit due to interactions with the early solar nebula, and then back out a little ways (imitating a tack, the maneuver where a sailboat changes direction).
Of all of the fascinating facts and theories involving the solar system, The Grand Tack hypothesis is one that is especially interesting to me. It describes Jupiter’s migration patterns during the early formation of the solar system where planets were still settling into stable orbits.
During all of this movement during our solar system’s formation, the theory discusses how this may have gravitationally interfered with another gas giant possibly ejecting it out into space as well as clearing out possible building blocks that Mars could’ve used to eventually gain more mass. All in all, it is a pretty widely accepted theory in the scientific community.
Discovered in 1930 by astronomer Clyde Tombaugh at the Lowell Conservatory in Arizona, Pluto has challenged the confines and definitions of how scientists classified objects within our solar system. Up until 2006 it was considered a planet but was then demoted to dwarf planet after scientific consensus that it does not clear its orbit of other objects (a defining characteristic of planets).
The mass of Pluto is only 0.2% of Earth’s mass and it’s diameter is roughly 1/6 that of Earth. It takes 248 Earth years to travel around the sun and is composed of rock and ice and also has 5 moons named Charon, Styx, Nix, Kerberos, and Hydra! It is also geologically active with ice mountains. Being the largest dwarf planet while also being the smallest planet (if you consider it to be), Pluto is unique within our solar system and brings to light the subjectivity of scientific classification and the ever changing nature of it.
Since its launch on December 25th, 2021 and arrival at its final “positioning” on July 11th, 2022 (Wikimedia, Timeline of James Webb Space Telescope), the James Webb Space Telescope (JWST) has made a myriad of revolutionary findings that challenge our previous understanding/theories of the Universe. Due to its intentional design aimed at helping us understand the diversity of galaxy compositions and structure over space and time (since we can look at galaxies that are so immensely distant) (WebbTelescope.org) and its ability to look much deeper into the cosmos, it has led to findings that force us to rethink the early universe and galaxy formation processes.
One of these discoveries were “red monsters” (Image 1), three ultra-massive galaxies that formed over 12.8 billion years ago (a few hundred million years after the Big Bang). The discovery of these contradicts the previously-existing models that claimed slow stellar formation(SciTechDaily, 2024). According to our theories before this discovery, galaxies of this size shouldn’t have been capable of forming so quickly after the predicted “birth” of the Universe. It suggests that star formation was far more efficient in the early universe than previously believed.
(Image 1 from Live Science, depicting the galaxies in question and their locations in the universe)
Another groundbreaking observation was looking at black holes that formed just 1.5 billion years after the Big Bang (more specifically LID-568, (Image 2)). These revealed an unprecedented rate of growth that challenged our current models in the same way that the red monsters did (Nasa.gov, 2024). Since the black holes were capable of “eating” so much more mass than scientists had believed prior, it suggests that our previous understanding of the mechanisms of black holes in the early universe may be incomplete. The understanding of how black holes of this size were able to form so massive and quickly is still unexplained, but we now have evidence indicating a gap in our knowledge (Space.com, 2024).
(Image 2 from Nasa.gov, an illustration of early-universe dwarf galaxies with black holes at their center that consume mass at rates much higher than previously believed)
The image of the Antennae Galaxies released May 19, 2008 NASA article. Please refer to this photo when reading the following blog post- specific aspects of the image are mentioned.
The Hubble Heritage Collection released a photo in 2008 that showed a shocking image of the Antennae Galaxies. While it may just look like a beautiful swirl of colors, the image actually shows a pair of merging galaxies. This is one of the nearest and youngest examples of this occurrence! I want to explain two major features of the photo. First, the orange “blobs” are the cores of the original galaxies. The dust from these appears brown in similar photos. Second, the “arms” in the photograph represent how the Antennae Galaxies received their name, but also the reaction of “tidal tails” when galaxies begin to encounter one another. Astronomers at NASA believe the Antennae Galaxies show a preview of what could happen when the Milky Way encounters the Andromeda galaxy.
Before the discovery of any exoplanets (prior to 1992), scientists hypothesized that star systems will planets (planetary systems) similar to our own solar system might exist around other stars– even without having confirmed evidence of them in the same way we do today. In some ways, they expected that these other planetary systems would likely follow the same general structures and creation process as our own: smaller rocky planets close to the star, and larger gas giants farther out. This was an assumption based on how our own solar system was formed, based on the guiding principle that we should not assume there is anything special/unusual about our own particular place in the Universe unless we have good reason to. As Richard Chapman from Spacelab Ireland stated in a forum post, “Our star has planets, therefore others probably do too” (Quora, 2021).
The first exoplanets were found orbiting a pulsar (Image 1), which is a rapidly rotating neutron star that blasts pulses of radiation at regular intervals (Space.com, 2023) rather than a typical star. In 1992, astronomers Aleksander Wolszczan and Dale Frail discovered two planets orbiting the pulsar PSR B1257+12, a confirmed discovery generally considered to be the first definitive detection of exoplanets (Wikimedia, Exoplanets, n.d.). Although scientists had expected other stars to have planets like our own solar system, they were not expected to be found around pulsars because pulsars are remnants of supernova explosions and were not thought to have planets. Nonetheless, these “pulsar planets” likely survived the supernova explosion or formed from debris that was left over after the supernova. In a way, the existence of these pulsar planets suggested that planetary formation was possible in diverse and extreme environments, which challenged the assumption that only Sun-like stars would host planets. Michael Mayor and Didier Queloz were the first to confirm the existence of an exoplanet orbiting a main-sequence star: 51 Pegasi b. This planet was discovered using the radial velocity (doppler) method, especially enabled by the fact that 51 Pegasi is a nearby star (50.91 light years away).
(Image 1 from CosmosAtYourDoorstep.com, Pulsars as Neutron Stars, depicting the key components of a pulsar)
Just over 6 years ago, the Chandra X-ray Observatory’s researchers combined a method we haven’t yet learned in class (microlensing) with the use of their observatory to find evidence of planets in other galaxies (which are much farther than the exoplanets inside our own galaxy). They stated, “Unlike Earth, most of the exoplanets are not tightly bound to stars, so they’re actually wandering through space or loosely orbiting between stars. We can estimate that the number of planets in this [faraway] galaxy is more than atrillion.”
Ending thought: During our class today (Tuesday, Nov. 12), Dr. Molina brought up the idea that it wasn’t until the early 1990s that the first exoplanets were actually discovered/proved, and this got me wondering: what did we (as in society, scientists, the knowledge at the time) think about exoplanets before we discovered any exoplanets?
A binary star system is a pair of stars which orbit a common center of mass. In fact, they are quite common in the universe.
Types of Binary Star Systems
Visual Binaries: Such a binary system can be resolved as two separate stars using a telescope.
Spectroscopic binaries: here, the components would be close enough to one another that it would not be possible to visually distinguish the two. The binary would have to be recognized as such through its spectrum from their combined light.
Eclipsing binaries: the stars in these systems periodically eclipse one another which causes changes in the brightness detectable by an observer.
Binary Star Systems and Planetary Formation
Being a binary star system, this can highly affect planetary formation and evolution. This is because normally, gravitational pull of the two stars disrupts the process of formation altogether, making the likelihood of the planets being in stable orbit around them pretty low. In a few cases though, a binary star system can be stable enough to host the process of planetary formation, especially around areas far from the primary stars.
