Ganymede, Aurorae, and the Potential for Life Outside of Earth

Posted on April 9, 2023 by groblesnieles727

Artist’s conception of Ganymede and Jupiter. Image by NASA

Although by visible light and upon first glance Ganymede might seem like an unassuming satellite, further inspection and deeper exploration demonstrates that this view is both tired and untrue.

Simply by size alone, Ganymede is a headliner. As the largest moon in our solar system, it exceeds in size Earth’s moon (obviously), but it’s also larger than both Pluto and Mercury–bodies which either have been, or are currently classified as planets. Though Ganymede doesn’t meet the three criteria to be classified as a planet (thanks, Jupiter), the size of this satellite is quite remarkable.

Beyond the matter of size, Ganymede is an anomaly within our system, in that it is the only moon known to have a magnetic field of its own.

Hubble image of Ganymede, with its auroral belts colorized in blue. Image by NASA/ESA

As demonstrated in the image above, the Hubble Space Telescope captured auroral belts on Ganymede, and what’s more, it noted that the aurorae are “rocking” back and forth to a degree that supports the conclusion that a massive salt-water ocean lies beneath the surface of the moon. This ocean, which is estimated to be ten times deeper than Earth’s oceans and contain more water than the entire surface of the Earth, was an exciting discovery in the search for life-sustaining worlds and life beyond Earth. According to NASA, a previously created model supports the idea that it would be possible for primitive life to develop in this ocean.

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I want to belive.. but I can’t!

Posted on April 9, 2023 by dougkyles422111
A poster popularized by The X Files

As I do so often, I would like to talk about the possibility of extraterrestrial life within the Universe. I will take this last blog as an opportunity to reflect on the things which I have been able to learn from the course as a whole as it relates to one of the topics I am most interested in. Ultimately, I hate to make this conclusion, but I believe that extraterrestrial life is likley, but we will most likely never reach any meaningful contact with them. I believe that it is likely simply from the vast scale of the universe. It is said by many leading astronomers that there are “billions” of planets like Earth. There is no reason we should be one of the only ones to possibly harbor life. While Earth’s situation is highly unlikely as a planet, the almost mathematically, and in reality practically, infinite number of systems suggests there are at least a handful of places similar to Earth in their ability to harbor life.  

While the possibilities for life are limitless, there are two main reasons I do not believe we will experience meaningful contact. First is the massive scale of the universe in general. The idea of physically transporting probes and even spaceships the distance to other stars, much less galaxies is a task that is seemingly impossible. Likely, if there was life somewhere out there, it wouldn’t have developed at the same time as our civilization. There would be a large portion that would have developed sooner, and these beings would have most likely discovered a way to communicate with us within their billions of years of development. So the second reason is the fact that we haven’t heard from anyone out there yet, because if they were truly out there, ​​someone would’ve most likely figured it out.

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The Cosmic Microwave Background

Posted on April 9, 2023 by constellationsarentreal

One of the pillars that the Big Bang Theory Model rests on is the existence and characteristics of the Cosmic Microwave Background (CMB). The CMB is an observed cosmic glow of radiation seen everywhere, filling the universe like a sea. Roughly 380,000 years after the Big Bang, the universe cooled enough (~3,000K) for free-roaming electrons to bind into atoms of Hydrogen and Helium, allowing photons to travel unhindered. As a result, light shot out everywhere, allowing the universe to become transparent.

Since then the universe has expanded in size by 1,000 times, meaning the CMB should appear 1,000 times cooler. Accidentally discovered in 1956, the CMB appeared to come from every direction. The measured thermal spectrum of the CMB revealed a temperature of exactly 2.73K, roughly 1,000 times less than the ancient temperature of the CMB, thereby supporting the Big Bang Theory. Even still, models of the Big Bang Theory predict a 7:1 H-He ratio in the era of nucleosynthesis (the first three minutes of the universe). Models predict that the current ratio should be 3:1. Observed amounts of H-He content in the current CMB show 75% H, 25% He, providing yet another line of evidence.

The above image was taken by the Planck Space Telescope and depicts the map of cosmic radiation left over from the Big Bang: the CBM! The image was gathered over several months from the oldest light in the universe. The map depicts slight temperature variations that correlate to denser regions of space during the early years of the universe. In other words, the CMB maps out all the dense regions that would later become stars and galaxies!

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Blog Post 6: Gravitational Slingshot

Posted on April 9, 2023 by Myles7235
Gravitational Slingshot

Have you ever played with a slingshot to shoot small items such as pebbles as a kid? Astronomers can also tap into their inner child by using a gravitational slingshot in space. A gravitational slingshot happens when a small object uses the gravitational pull of a larger object to speed itself up. Take a spacecraft as the smaller body and a planet as the larger body. When a spacecraft passes by a planet at a certain angle and encounters the planet’s gravitational attraction, the spacecraft can be shot forward with greater speed. It’s as if the planet is the slingshot and the spacecraft is the pebble. The key difference between a regular slingshot and a gravitational slingshot is that the spacecraft is stealing momentum from the spinning planet. Since the spacecraft ends up stealing some of the momentum of the spinning planet, the rotation of the planet slows down. The planets slows down by an extremely insignificant amount since it is much more massive than the spacecraft. To our eyes, the planet looks like it is moving the exact same speed as it did before. Although your traditional slingshot may not be as cool, you may one day be able to contribute to a space mission that uses a gravitational slingshot if you pursue astronomy!

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Pluto: If Size Doesn’t Matter, What Does?

Posted on April 9, 2023 by dougkyles422111
Protestors in Favor of Pluto’s planetary status. CNBC

Pluto is one of the most underestimated discoveries of our solar system. What we expected to be a simple ice ball comet-like object in the very outreaches of our solar system ended up becoming one of the most interesting planetesimals that tell us a complex geology category. Many will know Pluto for its classification as a planet, and then revocation of that category and the placement within a new one- dwarf planet. Ultimately, I was surprised to learn throughout namely chapters 11 and 12 that the boundaries of the terminology we use for solar system objects is quite arbitrary. There are always exceptions to the rule, for example as soon as we identified Pluto as a dwarf planet we posed the difficult question if the likely many many objects in the outer solar system are considered dwarf planets as well. When we look closely we can really only distinguish many of these outer objects by size, which is not a good differentiator because it is all relative. Many people are very heated in the debate on Pluto’s planetary status, with many (Like UTK’s Dr. Littmann) claiming we should keep it in the relatively arbitrary dwarf planet category for a unique reason: designating Pluto in this special category warrants it the attention it most likely deserves due to its unique geological story. This is a reason that I believe has some validity, but its irrelevance to the physical factors of Pluto essentially proves these categories are arbitrary.

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The Loneliness of Rovers

Posted on April 9, 2023 by 88bw
This is an illustration of what the Opportunity rover must have looked like as it traveled across Mars for 15 years.

Throughout this semester in ASTR2110, I have been reminded about how small we are compared to the universe. While this can be both a deflating and motivating perspective on our approach to astronomical study, I think it is undeniable that the rovers on Mars are unimaginably lonely during their stints on the red planet. I was reminded of these machines’ presence during a short YouTube video that shows the Curiosity rover singing itself “Happy Birthday” because it has no one else to celebrate with. It’s silly to anthropomorphize rovers that are tens of millions of miles away, but it makes me appreciate the work that the rovers do even more.

Curiosity was sent to Mars in 2012, and it’s nice to remember that for a few years, it got to share the planet with the Opportunity rover. The Opportunity rover is currently the standout success of our history with Mars rovers; Opportunity survived for nearly 15 years and may have lasted longer had a dust storm not covered the rover’s solar panels. While they never intended to cross paths, it is heartwarming to know that we have reached levels of success that ensure that we have at least two operational rovers on the planet now (Curiosity and Perseverance). I have wondered why NASA isn’t sending Curiosity to Opportunity’s site to help recover the hardy rover, but there are plenty of reasons. First of all, there is simply too much distance between the two rovers. Secondly, Curiosity was not built to be a rescue rover, so it may be futile in its rescue efforts if it ever made contact with Opportunity. Finally, astronomers have carefully planned out the missions and routes that these rovers take; a massive detour for Curiosity would ruin decades of planning behind Curiosity’s survey of Mars.

These sorts of thoughts confirm the amount of deliberation and careful planning that support the success of these rover missions. It would be wishful thinking to assume that these rovers can just roll about as they please, but it is a nice reality check to remember the precise commands and plans that govern the rovers that are the fruits of massive funding and human resources.

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Halley’s Comet

Posted on April 9, 2023 by sahilreddy2

Giotto Spacecraft Approaching Halley’s Comet

Halley’s Comet has the ability to completely destroy a city. Until learning about this comet in a previous homework assignment I never realized the true devastation even a comet of this size could cause on the earth. Halley’s Comet most famous observation occurred in 1066 where it was said that shortly before the invasion of England, William the Conqueror saw the comet and believed that it ensured their success in battle. Later as it was observed in the 1500s and 1600s, Edmund Halley in the 1700s determined that the comet would return every 76 years, and thus it was named after him once he passed away. When Halley’s Comet returned to earth in 1986, we were finally able to get proper images like the one above as we had spacecraft to take them. Also, once it returns in 2061 the comet will be on the same side as the sun and thus it will be much brighter than in 1986. Halley’s comet is one of the larger comets as it is about 15 miles in diameter, however because of the gravitational forces of the Sun and other planets it is very unlikely that it would ever impact any planet. Thus, these comets aren’t something we should worry about wiping us out as it is truly a miniscule chance that it would happen, and rather we should admire and observe them as they pass by us in the cosmos.

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The Outer Solar System

Posted on April 9, 2023 by dromalley
Pluto, formerly the 9th planet 😦

For this blog post, I’m going to be taking you on a journey through the outer solar system, beginning with what’s usually the last stop on the tour: Pluto. Pluto, formerly a planet, is now classified as a dwarf planet, orbiting at a distant 39 AU from the Sun in the dim outer reaches of the solar system. This region, known as the Kuiper Belt, is home to at least dozens of similar objects, with many more almost certainly lurking in the darkness.

Beyond the edge of the Kuiper Belt the solar system is largely devoid of anything until its boundary: the heliopause, the spherical boundary where solar radiation is in perfect balance with interstellar radiation. Beyond this, the occasional particles in the vacuum of space have an extrasolar origin, and it marks the boundary of interstellar space.

The Heliopause is the boundary between our Solar System and interstellar space

Even further than this, however, extending as far as 100,000 AU from the Sun according to some estimates, is the Oort Cloud, a spherical shell of small icy bodies whose existence is predicted to be the source of long period comets. These distant comets are the furthest objects still bound to our solar system, although at such extreme distances any connection is tenuous, and represent its final limit.

The Oort Cloud, the furthest objects “in” our solar system
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Naming Extrasolar Planets

Posted on April 9, 2023 by 88bw
This image by NASA shows 51 Pegasi b revolving around its sun, 51 Pegasi. They were discovered in 1995, and I see it as an example of an uninspiring, unversatile naming system.

Ever since we learned about the naming themes with the Jovian planets’ moons in class two weeks ago, I have been interested about how astronomers have managed to not run out of naming themes for the vast universe as they discover more worlds. I thought that the Jovian planets took up most of the cooler themes with Shakespeare characters and Greek deity relations. Meanwhile, I often come across extrasolar planets with relatively unappealing names that are nearly identical to their star(s), such as the example of 51 Pegasi and its planet in the picture above. There is actually a rhyme to the reason though; this NASA article goes into depth about the traditional naming system.

All planets have designations, but only a portion of the known planets get a proper name like Saturn or Neptune. The designation naming system is very straightforward; there usually is a reliable naming catalogue like the Henry Draper Catalogue, and stars are named in the order that they are found. For example, the 165,321th star to be discovered would be called HD 165321. From there, the planets that orbit the star can be named in the order that they are discovered using the alphabet. In this case, the star itself is considered “letter A” so the first planet to be discovered around HD 165321 would be called HD 165321 b. This raises the question of how they named planets that have more than 25 other neighboring planets in the same solar system, since you would run out of alphabets by then. In addition, this naming designation system also assumes (correctly) that in almost every situation, the star is discovered first followed by its respective planets.

It is exciting to see the article mention that the establishment of proper names is increasing in frequency. In fact, the article raised a naming contest as one such avenue for finding attractive proper names for planets that simply do not belong in our own solar system. I feel like these naming contests make astronomy feel more accessible to the common folk in an age where the communication of physics and astronomy is burdened by the barrier to entry of understanding the increasing levels of complexity in the fields. It harkens back to Dr. Tyson’s preface to our textbook where he emphasizes that the communication of science is of utmost importance in this day and age.

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It’s a bird! It’s a plane! No, it’s… Super Earth???

Posted on April 9, 2023 by groblesnieles727

Image by NASA https://exoplanets.nasa.gov/eyes-on-exoplanets/#/planet/GJ_15_A_b/

Within our solar system, there are three main classes of planets: terrestrials, gas giants, and ice giants. These planet types are reflected throughout the universe, with NASA categorizing these similar planets as gas giants (or Jupiter-analogues), Neptune-likes, and terrestrials (or Earth-analogues). However, within the universe, NASA also recognizes and classifies exoplanets within a fourth category: Super Earths.

Although the name seems to imply Earth-like characteristics, the Super Earth category only makes reference to the size of these planets. Super Earths can be as large as double the size of Earth, and ten times as massive. These planets can be rocky, gaseous, or some combination thereof, but the key detail is that they are smaller than Neptune-likes (although those on the extremely large end of the spectrum are sometimes referred to as mini-Neptunes or sub-Neptunes).

One such exoplanet is GJ 15 A b, depicted (hypothetically) above and discovered in 2014 by radial velocity. Although the category may have connotations of Earth-like characteristics, GJ 15 A b is only similar in that, dimensionally, it exists on a scale similar to Earth. Its radius is approximately 1.5 times that of Earth’s, and it is about three times as massive. However, its orbital period is extremely quick relative to Earth’s at only 11.4 days to orbit its parent star. Additionally, the surface temperature is described as super-heated, with NASA estimating its surface temperature at 530 degrees Fahrenheit.

Unlike Neptunians, Jupiter-analogues, and Earth-analogues, there is no planet in our system that fits the category of “Super Earth.” These planets could prove to be essential for research regarding planetary formation theories, but for now, we’ll have to settle for our own super Earth.

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