Ultima Thule

The New Horizons space probe was launched in 2006—primarily to study Pluto, but also to study Kuiper belt objects in its following years. Following the space probe’s flyby of Pluto in 2015, it reached 2014 MU69, also known as Ultima Thule, on January 1, 2019. Ultima Thule is a Kuiper belt object that orbits 1.6 billion kilometers beyond Pluto, making it the farthest object that has been visited by a spacecraft. That being said, it will take approximately 20 months for all the data gathered by the New Horizons probe to be sent to Earth, and all the data won’t be back until the summer of 2020. Here’s some of what we do know: The object is a “contact binary” made of two planetesimals that have been fused together, nicknamed “Ultima” and Thule.” It is approximately 31 kilometers long and has a red surface color. The two parts of the object seem to have orbited one another until they were merged together. New Horizons observations have shown that Ultima—the larger lobe—is flattened, and the smaller lobe—Thule—is more rounded, like a walnut. The unique shape of this object is unlike anything else that has been seen in the solar system so far, and it allows us to look into the earliest stages of planetesimal accretion and planet formation within our solar system.

New Horizons image of 2014 MU69 (Ultima Thule) – By NASA/Johns Hopkins Applied Physics Laboratory/Southwest Research Institute, National Optical Astronomy Observatory, Public Domain
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Io

Io

Io is one of the closest and most prominent of Jupiter’s moons. Surprisingly, Io has the most volcanic activity of any of the worlds in our solar system. Usually, people think of moons as large barren rocks (similar to our own) however, Io breaks that mold. Because Io has such a large amount of volcanoes, we know that its internal temperature must be pretty high. This high internal temperature is due to tidal heating. Jupiter exerts a great tidal force on Io due its large mass. This large tidal force added to the fact that Io’s orbit around Jupiter is somewhat elliptical means that the size and orientation of Io’s tidal bulges are constantly changing. The changing in these tidal bulges causes Io to experience a lot of internal friction, which is what makes Io have a very hot interior. Not only is Io’s internal temperature what makes it interesting, the fact that it has a slightly elliptical orbit adds to its uniqueness. Typically, a moon or other large body of Io’s size would have a nearly circular orbit. However, due to the gravitational tug between Io and Jupiter’s other large moons, Io is moved into an elliptical orbit.

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Eight Planets or Nine?

Most of us probably remember a time when the Solar System had nine planets, with Pluto as the ninth and (usually) farthest from the Sun. In 2006, following the discovery of Eris, the International Astronomical Union (IAU) voted to reclassify Pluto as a “dwarf planet” (don’t forget the quotation marks!). However, there might one day be a ninth planet yet again!

Artist’s conception of Planet Nine with the Sun and Milky Way in the background
Source: Nagualdesign and Tom Ruen via Wikimedia Commons

Astronomers have been searching for a possible Planet Nine beyond Neptune’s orbit ever since 2004, when the peculiarity of Sedna’s orbit was discovered. Sedna’s orbit (76 AU at perihelion) is farther out than can be explained by gravitational interactions with Neptune alone, hinting at an interaction with an unknown object. Ten years later, a similar case was discovered: another dwarf planet orbiting at 80 AU, too far to be explained solely by Neptune’s gravity. 

Even more recently, in 2016, two scientists from the California Institute of Technology (Caltech), Konstantin Batygin and Mike Brown, proposed a detailed hypothesis for the existence and characteristics of Planet 9. According to them, Planet Nine has the following characteristics:

  • Its perihelion distance is probably around 200 AU, but could be up to 350 AU.
  • Its aphelion distance (which is harder to determine) is between 500 AU and 1200 AU.
  • Its mass is at least 5x that of Earth, but likely around 10x or possibly greater
  • Its radius is about 2x-4x that of Earth
  • Its appearance is similar to that of Neptune

Notice that this proposed Planet 9 is incredibly far away! For reference, Earth orbits (by definition) at a distance of 1 AU, while Neptune orbits at around 30 AU. Considering that Planet 9 is around ten times farther from the Sun than Neptune (which we already cannot see with the naked eye), it is not surprising that we have not yet been able to detect this planet. Furthermore, it is quite probable that Planet 9 is currently at aphelion, making detection even more difficult (especially due to the Milky Way Galaxy in the background), considering that it would likely be fainter than a 22nd magnitude star. However, a number of powerful sky surveys have ruled out areas where Planet 9 isn’t, and hopes are high that in the near future, more survey data will be able to pinpoint the location of this mysterious planet! If so, I feel it will be one of the most exciting astronomical discoveries in our lifetime!

Do you think there’s a planet Nine out there?

Sources:

“Planet Nine.” Wikipedia, Wikimedia Foundation, 28 Mar. 2019. Web.

Batygin, Konstantin, and Mike Brown. “The Search for Planet Nine.” The Search for Planet Nine, 1 Jan. 1970. Web.

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Extrasolar Planets: A Search to Span Solar Systems

Recently, I have started work as an undergraduate research assistant in the Physics and Astronomy department at my university. The project I was assigned to is of a stellar nature; we are attempting to find evidence of extrasolar planets, or planets around other stars. Though we haven’t found any planets yet, I keep thinking about how crucial this type of work is to the future of the human race. Around 4,000 extrasolar planets have been confirmed by NASA, and it is amazing to think that one of these could be humanity’s next home. In this blog post, I will discuss the major approaches that astronomers use to detect planets outside of our solar system.

The Astrometric Method: Using the astrometric method, we can detect extrasolar planets by carefully monitoring small changes in the host star’s position in the sky. Planets orbit their host stars because of the enormous amount of gravitational force exerted on them by their stars. However, the laws of physics tell us that the planets also exert an equal amount of gravitational force on their host star. Though the star is much more massive, the planets can cause a star to “wobble” as it is gravitationally tugged at. Very few extrasolar planets have been identified using this method; the star studied must be relatively near to us, and observing positional changes may require long periods of observation.

Image Source: Wikipedia

The Doppler Method: Like the astrometric method, the Doppler method relies on the gravitational interactions and “tugs” between a host star and its planets. When a star is moving towards or away from us, we say that its light spectrum is blueshifted or redshifted, respectively. Alternating blueshifts and redshifts relative to average Doppler Shift can indicate a star’s motion or “wobble” due to its interactions with a planet or planets. The Doppler method has discovered many more extrasolar planets than the astrometric method, but it certainly does not come without its limitations. This technique is best suited for massive planets with close orbits, and because it calls for stellar spectra, large telescopes and long periods of observation are a must.

Image Source: EarthSky

The Transit Method: When an extrasolar planet’s orbital plane is situated along our line of sight, the planet will appear to travel in front of its star once every orbit. Astronomers call this a transit event. Similarly, half an orbit later, the planet will become eclipsed by its host star as it passes behind. We can detect these events by monitoring changes in the star system’s brightness. During a transit event, the star undergoes a characteristic dip in brightness as the planet blocks some of its light. During an eclipse, there is a dip in the system’s infrared brightness as the star blocks the infrared light emanating from the planet. Most extrasolar planets have been discovered using this method, but it is only feasible for planets with orbital paths that are oriented in just the right way.

Image Source: National Aeronautics and Space Administration

Direct Detection: This technique involves acquiring images or spectra of the planet. In theory, this is the best way to learn about an extrasolar planet; however, our current technology can only produce images with low resolution. There are other obstacles to directly detecting planets as well. For one, stars give off much more light than any planets that might be orbiting them. Because of diffraction, our telescopes also blur star light. Most extrasolar planets are too close to their bright host stars to be imaged directly from our vantage point, light years away. Second, compared to massive stars and the colossal distances between them, planets are miniscule.

An infrared image of a brown dwarf and an extrasolar planet (bottom left corner) located about 230 light years from Earth. Image Source: Slate
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Halley’s Comet

In 2061, Halley’s Comet will return to pass by Earth in 75-year long round trip across the solar system. But what else do we know about this mysterious visitor?

Studying the reports of comet sightings in 1531, 1607, and 1682, Edmond Halley deduced that these comets were in fact the same one and that it would return in 1758. Though Halley died in 1742, the comet did indeed return in 1758 and was named after its discoverer. When Halley’s comet returned in 1986, technology had finally allowed astronomers to study it. Probes from multiple international space programs were sent take close-up pictures of the comet for the first time. Research has shown that Halley’s comet is slowly losing about a thousandth of its mass with every loop around. Although it will still take thousands of years to finally die out, it is disheartening to see that not all things in the universe are permanent.

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Enceladus

The Surface of Enceladus, captured by the Cassini spacecraft
Source: NASA via Wikipedia

Enceladus is a medium-size moon of Saturn, with a diameter of about 500 km. Its surface temperature is quite chilly, ranging between 32.9 K (-240 degrees Celsius) and 145 K (-128 degrees Celsius); this is partially because of its distance from the Sun, and also because of its highly reflective surface. The entire moon is coated in fresh ice, so it reflects a lot of the sunlight that reaches it. This helps make it cold, and also makes it one of the brightest worlds in the solar system. Despite its small size and its frigid surface temperatures, Enceladus seems to show signs of ongoing geological activity, due to the fact that its orbital resonance with Dione (another of Saturn’s moons) causes tidal heating.

One of the most fascinating things about Enceladus is that it is believed to have a global subsurface ocean of water beneath its coating of ice. Thanks to tidal heating, Enceladus spews geysers of its ocean material from near its South Pole. The Cassini spacecraft found that these geysers contain mostly water vapor, along with traces of nitrogen, methane, and carbon dioxide. The geysers reach hundreds of miles into space, and the released material makes up most of Saturn’s E ring.

Cassini image of Enceladus, backlit by the Sun. Illustrates how far the geysers reach.
Source: NASA

The presence of liquid water and other compounds have led many to speculate/wonder if Enceladus is capable of sustaining some form of life in its ocean. Programs such as the Breakthrough Initiatives and other proposed missions such as the Enceladus Life Finder seek to find whether life does exist somewhere on Enceladus.

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Blog 5: TESS


NASA’s new exoplanet telescope, the TESS (Transiting Exoplanet Survey Satellite), was launched April 18, 2018 and is expected to find 20,000 exoplanets during its 2 year primary mission. This is huge increase compared to the 3,933 that are currently confirmed. Among these planets will hopefully be multiple rocky planets in the habitable zone, or zone where liquid water can exist. TESS is sensitive enough to see planets a little bigger than Earth for perhaps 1,823 stars and Earth sized ones for 408 of them. In an article by NASA, Lisa Kaltenegger is quoted explaining that “life could exist on all sorts of worlds, but the kind we know can support life is our own, so it makes sense to first look for Earth-like planets,” thus explaining why the data of these planets in the habitable zone are garnering special attention.

A fascinating detail about the TESS satellite is its orbit. It is in a highly elliptical orbit that’s apogee is almost as far away as the moon and perigee that comes as close as 108,000 km (about 3.5 times closer). TESS is in a 2:1 resonance with the moon, meaning that it orbits the Earth twice for every moon orbit, and is timed to be about 90° away from the moon thus minimizing the moon’s interference in TESS’s orbit.

TESS’s past orbits and current orbit

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A Moon Above the Rest: Jupiter’s Moon Ganymede


Jupiter’s Moon Ganymede

Galileo Galilei discovered many “luminous objects” in 1610 that were orbiting Jupiter. Thought to be stars, it was discovered that they were moons: Io, Europa, Ganymede and Callisto. Ganymede is the largest moon in the Solar System and is even larger than the planet Mercury. It is the only satellite in the Solar System known to possess a magnetosphere, has a thin oxygen atmosphere, and could have an interior ocean. There have been flybys and probes orbiting Jupiter since the 1970s that approach the moon to learn more about it. The most interesting fact to me about Ganymede is its name and mythological reference. It is named for the mythical Greek son of a king who was taken by Zeus, also known as Jupiter, posing as an eagle. On Mount Olympus, Ganymede won the position of cub bearer to the gods, and stayed on also as the favorite companion to Jupiter also known as Zeus. The more you know!

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Asteroid Defense Systems

As it currently stands, Earth has no recourse if a large asteroid decides to strike. Something on the scale of the Cretaceous-Paleogene event would devastate humanity. So, how do we protect ourselves against such an impact?

Space.com

Enter NASA and the “National Near-Earth Object Preparedness and Strategy Plan.” According to them, five steps need to be taken to ensure some form of security:

  1. Improving Near-Earth Object Dectection
  2. Accurately predicting NEO behavior with modeling
  3. Creating technologies to deflect incoming NEOs
  4. Form international cooperation to further these goals
  5. Have emergency action plans in place for potential impacts

These goals are surprisingly attainable. Technology already exists that could potentially be used to guide asteroids away from Earth. In earlier plans, some spacecraft would be launched at an incoming object to change its course enough to make it miss Earth. Road blocks come in the form of funding, government approval, and cooperation from other space agencies around the world. However, this is a problem that needs to be solved as soon as possible; if we wait until an object is on course to strike Earth, we likely won’t have time to stop it.

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Why is Titan Special?

Gattaca (from: Youtube)

If you are a Sci-fi fan like me, you might be able to recall Vincent hiding his identity for the trip to Saturn’s moon Titan in Gattaca.

Star Trek 2009 (from: Youtube)

In Star Trek 2009, Kirk and Spock beam abroad the Romulan ship attacking Earth, while Enterprise hid itself in Titan’s clouds.

Avengers Infinity War (from: Youtube)

Or at least you should remember the battle on Titan (which is an exoplanet based on Saturn’s real-life moon Titan) in Avengers: Infinity War

In fact, Titan has shown up more than once in the Star Trek series as well as in other famous films, novels, and comics. Why always Titan?

What makes Titan exceptional among more than 150 known moons in the Solar System?

  • Titan is the largest moon of Saturn and the second largest moon in the solar system—larger than the planet Mercury.

Titan has a radius of about 1600 miles, which only is 2.5 times smaller than the Earth. The largest moon in the Solar System, Jupiter’s moon Ganymede, is only larger by 2 percent.

  • Titan is the ONLY known moon with a substantial atmosphere in the Solar System.

According to observations from the Voyager space probes, the atmosphere of Titan is thicker and denser than the Earth’s! Its atmosphere is also the only nitrogen-rich dense atmosphere in the Solar System aside from the Earth’s. On Titan, the air is dense enough that you can walk on its surface without a spacesuit. However, you do need an oxygen mask and special suit to protect you from its temperature of -290 °F. Atmospheric methane creates a greenhouse effect, which keeps Titan’s surface from becoming even colder.

  • Other than the Earth, Titan is the ONLY object in the Solar System known to have liquids on its surface.
Near-infrared radiation from the Sun reflecting off Titan’s hydrocarbon seas (from: Wikipedia)

There are rivers, lakes, and seas of liquid methane and ethane on Titan’s surface. Although the surface of this icy world is covered by a “golden hazy atmosphere,” the Cassini-Huygens mission discovered liquid hydrocarbon lakes in Titan’s polar regions. Titan has an Earth-like liquid cycle, which includes raining, filling of the water body, and evaporation. Scientists also suspect that its volcanoes release water instead of molten rock lava. There is also speculation that Titan has a subsurface ocean of water according to the gravity measurements.

  • Titan is considered one of the most habitable place in the Solar System.

The information above reveals Titan’s potential for harboring life forms that can survive in the surface hydrocarbon liquids or the subsurface ocean. Although there’s no evidence of life on Titan so far, it is definitely worth further exploration due to its unique features.

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