One of the most interesting bodies in the universe is the brown dwarf, a small world a few times the size of Jupiter. These are interesting because they do not fit cleanly into our definitions of stars and planets. They are technically under the category of star, but this is due in most part to the way in which they form. They form just as stars do, by accumulating gas in space following a disturbance in a nebula, rather than from the debris surrounding a star. However, because of their lack of gravity from their small mass, they have limited fusion in their core, meaning they are kept rather cool, and so, do not glow particularly bright. This is where they get their namesake, and also why they were not discovered until 1994.
Triton stands out amongst most moons. Usually a moon is made of the leftovers from when the solar system was being formed, ideally becoming large enough to force itself into a spherical shape. More ambitious moons are made directly from planet material cast off in an accident. Triton sticks out; it is theorized to have been thrown out of its original orbit in the kuiper belt. The high inclination it cycles Neptune’s equator is largely unique to it, and it orbits in the opposite direction Neptune spins. As a side effect to its origins, Triton was once far more geologically active than most moons of its size. This can be attributed to the once elliptical orbit Triton had, which affected the tidal forces on it, and the faster rotation it surely used to have.
When someone mentions Pluto, most people’s minds instantly go to the “Is Pluto a planet debate”. In fact, all I knew about Pluto before reading these chapters was that it was too small to be a planet. If you asked me to picture Pluto, I would have said something akin to our moon – rocky, filled with craters, and relatively boring. However Looking at the images of Pluto taken by New Horizons tells a different story. Filled with vibrant red patches, towering mountains, and massive glaciers, Pluto is the opposite of boring. In addition, un-cratered areas found on Pluto show that there is actually geologic activity happening, unlike the moon. Even Pluto’s moon Charon is much more interesting than our moon, as it too shows signs of geologic activity and a lack of craters on its plains. Finally, scientists now believe Pluto has a massive ocean running underneath it, similar to Jupiter’s moon Europa. Regardless of it’s contested planetary status, Pluto remains one of the most interesting bodies in our Solar System, and I hope we send another satellite back to do further research.
Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with color data from the spacecraft’s Ralph instrument to create this enhanced color global view of Pluto. Source
Pluto’s as a planet is very intriguing. Despite being located far from the Sun; Pluto has seasonal changes due to its tilted axis (just like earth!) and highly elliptical orbit. When Pluto is closer to the Sun in its orbit, the frozen nitrogen, and methane on its surface can temporarily sublimate, creating a thin atmosphere. This atmosphere can lead to the formation of haze and clouds, which is a reason on why Pluto appears reddish. However, as Pluto moves farther from the Sun, its gases refreeze, and the atmosphere collapses back to a thin layer of frost on the surface. The surface of Pluto is diverse as it has plains, mountains of water ice, and regions covered in tholins (uv light hitting carbon), which is a mixture of complex organic compounds that give the surface its reddish appearance. The most famous feature on Pluto is the heart-shaped Tombaugh Regio, a plain named after the discoverer of Pluto, Clyde Tombaugh. This region is a very new surface feature, that was most likely formed by the convection of nitrogen ice. Pluto’s terrain and weather is very dynamic, despite its small size and large distance from the Sun, it remains to have unknowns that interest lots of Physicists today.
One thing from this unit I found interesting was learning about extrasolar planets. The Hubble Space Telescope was the first to detect an exoplanet’s atmospheric conditions and collect data about its makeup. In 2000, Hubble was used to study the exoplanet 209458 b which was the first extrasolar planet that was known to make transits across its host star.
One notable discovery by Hubble is the TRAPPIST-1 planetary system which contains seven Earth-sized planets. All seven of the planets orbit closer to the host star than Mercury orbits our Sun! The planets are also orbiting very close to each other. This means that if you are standing on any given planet, it is possible that you could see clouds or geological features on the neighboring planets!
Since the TRAPPIST-1 star is an ultra-cool dwarf, it is possible that liquid water could survive on some of the planets. Planets e, f, and g are in the habitable zone, which is where temperatures are optimal for liquid water to exist on the worlds’ surfaces.
Based upon the formation and evolution of the rocky terrestrial planets, size of the planet results in whether the planet is geologically active or dead. However, the moons of Jupiter, Saturn, and Neptune are smaller in size than Earth, yet are geologically active. How come?
It turns out that the magma volcanic activity of the rocky planets can be replaced with liquid volcanic activity of water and ice. For example, Europa, despite being smaller than the Moon (hence, should not be geologically active) happens to be less cratered than the Moon. So, its surface is younger than the Moon which means that the surface must be continually repaved. We know that Europa is an icy moon. So, Europa must have an ocean of water underneath the surface layer of ice. So, whenever the surface layer of ice breaks off, the ocean underneath replaces that surface, somewhat analogously to how our injured skin might be replaced or “healed” by the skin underneath it. How does Europa have a liquid ocean? Well, due to tidal heating, Europa’s inner ocean is liquid. Furthermore, we know that Europa’s ocean is salty because Europa has a magnetosphere! Recall that a magnetic field can be created by accelerating charged particles. The rotation of the Europa rotates the salty ocean, containing positive charged sodium and negative charged chlorine ions. Hence, the acceleration of the charged particles leads to the creation of a magnetic field.
The big characteristics of Europa are similar to the big characteristics of Earth! The lack of craters, liquid stuff, and the existence of a magnetosphere are similar characteristics between Europa and Earth. Despite the drastically different composition of Europa from Earth, Europa and Earth have some similar structures that help govern how the moon operates. The rotating, liquid stuff (molten lava in Earth and salty ocean in Europa) helps create a magnetosphere.
On October 19th, 2017, a telescope at the University of Hawaii, called Pan-STARRS1 detected an object unlike any before observed in our Solar System. It was highly elongated (by a ratio of at least 10:1), completely inert (no dust floating around or behind), and composed of rock and possibly metal. Based on this makeup, and the fact that it was not observed to have any water or ice, the initial appearance was that of an asteroid. However, its trajectory and varying speed was more akin to a comet. Eventually it was determined that, in fact, the object Pan-STARRS1 was observing was not from our Solar System at all. It would come to be named ‘Oumuamua, meaning “A messenger from afar arriving first,” in Hawaiian. Prior to encountering our Star system, ‘Oumuamua was roaming the Milky Way, not in the orbit of any star for some time. We are still unsure of its precise origins – and it will be difficult to pin down, as ‘Oumuamua is not in orbit around our Sun, either — it was simply a visitor. With roughly one extrasolar object passing through the inner solar system every year, though, it is only a matter of time before we learn much more about these fascinating visitors.
Alien life could very well be found in our own Solar System, and Europe is a prime candidate! Being one of Jupiter’s moons, Europe is one of the coolest moons of the giant planets in our solar system. It is about 90% the size of our Moon, with an equatorial diameter of 1,940 miles. However, if we replaced Europa with our Moon, it would be much, much brighter as its surface is made of water ice so it reflects 5.5 times the sunlight that our Moon does.
The surface of Europe is also one of the smoothest in our entire Solar System and has streaks and cracks on its ice which are caused by the large tidal forces from Jupiter. These tidal forces are also what is expected to be responsible for the geothermal heating that allows for Europa’s subsurface ocean to be in a liquid state.
Out of all of the moons and planets in our solar system, Europa has one of the strongest potentials for life due to the subsurface ocean that exists below the moon’s icy shell which also helps protect from radiation. The Hubble Space telescope also observed water vapor plumes coming from Europe, further solidifying this theory.
Future missions to this moon include NASA’s upcoming Europa Clipper and ESA’s JUICE mission. Specifically, the Europa Clipper is a spacecraft specifically designed to observe Europa thoroughly. This spacecraft will make almost 50 flybys of Europa at closest approach altitudes as low as 16 miles above the surface to scan nearly the entire moon. Its magnetometer will study Europa’s magnetic field, with a goal of confirming that Europa’s subsurface liquid ocean exists, as well as measure its depth and salinity. Hopefully, from this mission, we will gain an even better understanding of this fascinating Moon which could one day lead to the finding of alien life!
Titan is a commonly forgotten about moon in our solar system. It is the second largest moon that orbits Saturn. There are a few interesting things about Titan. Titan is one of the most Earth-like worlds found to date. Titan’s atmosphere is comprised of mainly nitrogen (95%) and some methane (5%). However, why it is unique is that there are organic molecules such as carbon and hydrogen in combination with the ice on the surface are similar to what is found Earth and are quintessential for life. Although Titan is too far from the sun right now (and thus too cold), in 6 billion years or so when the sun becomes a red giant the conditions will be amicable to for some forms of life. Only time will tell whether this is true or not, and unfortunately it will not be during our lifetime.
The idea for the telescope first came around in the 1940’s! Nearly 100 years ago, a scientist wrote a paper about the advantages of having a big telescope out in outer space, and they were right! Work on the telescope didn’t then begin until 1974 but the idea had been in place for decades. The telescope officially launched in early 1990 and for the past 30+ years, it has been providing us with great pictures of deep space and numerous insights.
What’s fascinating is how and why the telescope works. The reason telescopes work so well in outer space, hence the reason the aforementioned paper was written, is because the Earth’s atmosphere blocks some wavelengths, and the Hubble Telescope orbits outside of Earth’s atmosphere and can therefore get clearer shots. This coupled with the fact that it can focus without moving 7/1000 of an arcsecond while orbiting Earth at 17,500 makes for some very impressive imaging!
