In the center of the galaxy M87, stars seem to orbit an invisible object. By observing the path of the stars, scientists concluded that there is a supermassive black hole that is dense enough to cause these motions. Although the black hole itself is invisible, we can still observe the ring of light bended by the gravitational lensing. A telescope of the size of the Earth is needed in order to take a picture of the light 55 million light years away, but scientists managed to combine images taken from eight observatories around the globe.
Eight radio observatories teamed up in 2017 to work together as a global telescope, called the Event Horizon Telescope network. (from: Science News)
As the Earth rotates, telescopes in these locations are able to observe different part of the image. The researchers then developed imaging algorithms that can fill in the missing gaps in the measurements, “just as a forensic sketch artist uses limited descriptions to piece together a picture using their knowledge of face structure. (How to take a picture of a black hole-Katie Bouman)”
On April 10th, the first picture of a black hole was finally released by the Event Horizon Telescope team. This supermassive black hole 6.5 billion times more massive than the Sun was named Powehi (Po-veh-hee), which refers to “the adorned fathomless dark creation” or “embellished dark source of unending creation.” This image provides the strongest evidence of existence of black holes for the first time. It also confirms the prediction of the shape and glow of a black hole based on Einstein’s general relativity—Einstein is proved right again.
While talking about the search for extraterrestrial life, you may notice the difficulty in drawing a line between the living and nonliving. Bacteria are considered life forms, but viruses are not. Artificial Intelligence is able to do a lot of things that human beings can do, but it is not viewed as life by the general public…so what is life after all?
According to our textbook, there are six key properties for life: order, reproduction, energy utilization, response to the environment, and evolutionary adaptation. Examining those properties, we can easily rule out some suspicious candidates: viruses don’t have orderly arranged molecules; Artificial Intelligence also do not have cell structures.
However, as biologists regard evolutionary adaptation as the most fundamental property, the definition of life can be simplified as “something that can reproduce and evolve through natural selection.” Under this definition, all physical entities that have self-sustaining processes can be called life. For example, Artificial Intelligence, which has been a popular topic in recent years, might be considered as “artificial life” that can reproduce and evolve in the form of codes.
Now that the definition of life has become more generalized, can we view AI as an advanced life form that has never appeared on Earth before? If we take this different point of view, is cell-based life only a part of the spectrum of life? Maybe we are just in a phase of Earth’s history that life with cell structures are dominant. Then, in the search for extraterrestrial life, what are we really looking for?
What is the Fermi Paradox? In the most basic sense, the Fermi Paradox addresses the contradiction for the high likely hood of extraterrestrial intelligent life and the absence of any communication with our planet. Physicist Enrico Fermi asks the extremely thought-provoking question, “Where is everybody?”. While there are a number of interesting theories and possibilities that attempt to account for this mystery, I will only touch on a few. One rather grim possibility that seems to be more and more likely these days is concept of the Great Filter. From the math side of things (using conservative estimates) it is estimated that in our galaxy alone there should be 1 billion Earth-like planets and 100,000 intelligent civilizations. So why hasn’t at least one of these theoretical civilizations contacted us yet? While its certainly possible, in my opinion, that they tried a long time ago but we couldn’t document it, they don’t want to contact us for some reason, or they are contacting us but our technology is too underdeveloped to even realize it, I don’t know if that’s the case. This overall lack of communication is likely indicative of a filter, or some sort of trip wire that humanity hits where it ultimately destroys itself. While this Great Filter may have been the start of life itself or the jump from prokaryotic to eukaryotic cells, meaning we are the only ones who have passed it (crazy, right?), it seems a bit more likely that we are approaching it. A rather demotivating view, the current state of humanity and our impending destructive nature may be suggestive of end to our quest to colonize the galaxy. Thus, as intelligent life developed and reached a point where it pondered its own rarity in the universe and tried to expand to Type II and III civilizations it was always met with that filter of some sort. While this undoubtedly puts a cap on our ability to accumulate knowledge of the universe, it would explain the fact that no one has contacted us yet. Whether we are in a simulation or we are the only ones in the universe, there has to be more answers out there and hopefully some of those are uncovered in sooner rather than later.
The future of exoplanet research means not just the discovery of more exoplanets, but characterizing them. To do so, the European Space Agency (ESA) is launching the Characterizing Exoplanet Satellite (CHEOPS), the PLAnetary Transits and Oscillations of stars mission (PLATO), and the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey mission (ARIEL).
CHEOPS will observe bright stars with known exoplanets, in search for transits. The goal is to measure precise sizes of smaller planets and determine their densities (using mass data from other observatories). PLATO, however, will discover new planets with an emphasis on habitable planets where liquid water can exist on the surface. Additionally, it will analyze host stars to further our understanding of the extrasolar system’s evolution. Lastly, ARIEL will analyze the atmospheres of exoplanets. Altogether, the hope is to discover new life in the Universe.
An artist’s rendering of an exomoon, its host planet and star, from Sky and Telescope
What are exomoons?
Well, we have already studied exoplanets (short for extra-solar planets) which are planets that are not from our star system. Accordingly, exo-moons are moons that orbit planets that orbit stars that aren’t the Sun. Sounds pretty cool, right? Well exomoons get even more interesting. In fact, exomoons are currently the subject of intense research because scientists believe that they could be the next life-harboring world.
But why are scientists (seemingly) more interested in exomoons than plain old exoplanets? As it turns out, it is much more likely that we will find a moon with a similar mass, composition, and distance to the Sun than we will a planet. Earth-like planets might be more of a rarity among other terrestrial worlds, but just imagine the moons around gas giants! Even in our own Solar System, a few moons of the gas giants offer promise of liquid water and internal heating. Also recall that (we believe) gas giants are capable of migrating closer to their central star. Combine these two principles and we might just have the recipe for comfortable, water-filled exomoons in other star systems.
The main difficulty when it comes to exomoons is detecting them. It is already difficult enough to detect exoplanets (via transit method, Doppler shifts, etc). The detection of exomoons relies on much of the same principles, but requires much greater levels of precision.
What’s so great about a red spot? Well, the size of this spot, a massive storm in Jupiter’s atmosphere, is even larger than twice Earth’s diameter and is the largest of our solar system. Not only is it the largest, it has been consistently present for the duration of our usage of telescopes in observing Jupiter. Although it has only been studied since 1830, many descriptions of visible observation of the storm existed from as early as 1665, indicating that the monumental storm has likely existed for at least 350 years.
The long-lived storm that has occupied Jupiter’s atmosphere for so long possesses many similarities to a hurricane. The main difference stems from the fact that this storm’s winds circulate in a high-pressure system rather than a low-pressure cyclone. The spot’s red coloration has remained a mystery to scientists given the difficulty in its accessibility. However, it has been theorized that the pigmentation comes from a chemical reaction between contents of the storm in the atmosphere and solar ultraviolet light. Whatever the cause is, Jupiter’s Great Red Spot is the most unique and impressive storm in our solar system and certainly warrants further investigation.
1950
DA is an asteroid that was discovered in 1950 (hence the name) by Carl A. Wirtanen.
After it was first discovered, it was lost after 17 days of observation because
the period was too short to determine the asteroid’s future location. It was
rediscovered in December 2000 and recognized as 1950 DA in January 2001. It is
classified as both a near-Earth
object (NEO) and a potentially
hazardous object (PHO). Based on the definition of a NEO, 1950 DA’s
perihelion is less than 1.3 AU. The definition of a PHO tells us that 1950 DA
makes exceptionally close approaches to Earth (mimimum orbital intersection
distance of less than 0.05 AU) and is large enough to cause significant damage
in the case of an impact. This asteroid is also classified as an Apollo object, which details
that it has a semi-major axis greater than that of the Earth but perihelion
distances less than Earth’s aphelion distance. Apollo objects currently make up
the largest group of NEOs.
There
are two main things that I think make this asteroid very interesting. The first
thing is the fact that it is a PHO. After observations were made and analyzed,
it was determined at one point to have the highest probability of impacting
Earth. In 2002, it had the highest Palermo
rating for a possible collision in 2880. The Palermo rating scale is used
to rate the potential hazard of impact of a NEO. In addition to this, I also
think its composition is interesting. In 2014, physicists from the University
of Tennessee found that it is not a single continuous object, but actually a
mile-long collection of rocks held together somehow. They determined that the
body was held together by weak electrical attractions between the molecules of
the rocks, showing that Van der Waals forces
are the reason the form is held.
One of the best getaway scenes in movie history is in The Empire Strikes Back, when Han Solo navigates the Millennium Falcon through an asteroid field, with TIE Fighters in hot pursuit.
The scene starts with the Falcon getting hit by two asteroids. The asteroid field appears to have thousands of asteroids all flying around as far as the eye can see. The asteroids range in diameter from small rocks to the size of a small city. Han successfully navigates the asteroids while the Imperial fighters get pulverized by the rocks.
Star Wars’ portrayal of the asteroid field propagates a common misconception about the likelihood of colliding with, or even encountering, an asteroid.
As a bonus, I figure out how much kinetic energy the space rocks would carry in our solar system and the equivalent force in TNT.
What are the odds?
NASA’s Dawn Mission FAQ estimates the the volume of the Asteroid Belt is 16 cubic AU. An AU is the distance from Earth to the Sun. NASA estimates that there are 2 million asteroids greater than a mile in diameter within the asteroid belt. If the asteroids were distributed evenly, the distance between the asteroids would be about 1.9 million miles. This is 760 times the distance from NYC to Los Angeles.
A spacecraft has almost no chance of getting hit by an asteroid. In fact, it would be hard for someone sitting in a spaceship to see an asteroid with their naked eye. If the spacecraft was NYC, the nearest asteroid could be hundreds of Los Angeles(es) away.
What is the damage?
An asteroid does not have to be a mile long to inflict catastrophic damage to a spaceship. Imagine a space probe in our own solar system (miraculously) collides with an asteroid similar in size to the asteroids that hit the Falcon. Let’s calculate the kinetic energy of one of these tiny asteroids, and the equivalent force in kilotonnes of TNT.
What do we need to know for this calculation (we will use mks units):
Asteroid Shape: The asteroid definitely looks like a potato, but for math’s sake, I am going to pretend the asteroid is a perfect sphere.
Asteroid Diameter: The Millennium Falcon is about 35 meters in length. Since the asteroids were a bit smaller, we will use a diameter of 30 meters, and a radius of 15 meters.
Orbital Distance: Many asteroids orbit at 2.4 AU. This is 3.9E11 meters.
Asteroid Density: Average of 2g/cm^3 is 2000 kg/m^3
Now we do the math (on a separate sheet of paper):
Circumference of Orbit =
Orbital Period =
Avg Orbital Speed =
Asteroid Volume =
Asteroid Mass =
Kinetic Energy =
We got an answer! A spherical asteroid travelling at 3000 m/s should carry a kinetic energy of 2.8 quadrillion joules. This is equivalent to 2800 terajoules (a standard for nuclear weapon yields). For comparison, the Ivy King was the largest pure-fission bomb tested by the US, and yielded about 2100 terajoules.
Conclusion
Asteroids are incredibly deadly, even the extremely tiny ones. But, the odds of getting hit by one is astronomically low. You could fall asleep in an asteroid field expect to never get hit. Try not to dream about nuclear space rocks.
Comets have been noticed by ancient civilizations for millenia, and, like many other celestial bodies, were viewed as omens of the future. Comets in particular were considered bad omens. The most famous example is Halley’s Comet, seen in 1066 by the English and theorized to have been an omen for Harold II of England’s death. That same sighting must have been a good omen for his conqueror, Willaim the Conqueror! A comet also “heralded” the death of Julius Caesar, solidifying his deific status to the Romans. Napoleon on the other hand, believed that the appearance of comets was somehow linked to his early military victories. From 1200 to 1650 AD, comets were considered a herald of doom by Europeans. Gotthard Arthusius, a European historian in the 1600s, prophesied that a comet that he saw in 1618 would cause “earthquakes, floods, changes in river courses, hail storms, hot and dry weather, poor harvests, epidemics, war and treason and high prices”. Hilariously, European scholars had deduced by 1700 that such phenomenon were bound to occur regardless of the presence of a comet. Europeans in the 17th century used to believe that comets had some effect on the weather and thus their crops. It was not until 1950 that Fred Lawrence Whipple proposed that comets were in fact comprised of rocks and ice, and astronomers confirmed his theory in 2014 when frozen gasses were discovered surrounding comets C/2014 F6 (Lemmon) and C/2012 S1 (ISON).
Labelled diagram of Jupiter, including pink region theorized to be metallic hydrogen. Source: user Kevinsong on Wikipedia Commons
Hydrogen is the most abundant element in the universe, but at most reasonable temperatures and pressures it presents itself as an (infamously) flammable, colorless gas. In the high-pressure environments of the interior of Jupiter and Saturn, however, hydrogen takes on a rare and mysterious form: metallic hydrogen.
You’re probably familiar with the three traditional states of matter: solid, liquid, and gas. Water can take any three of these forms in our everyday experience, but hydrogen’s boiling and melting points are far lower than that of water. At standard pressure, hydrogen transitions from gas to liquid at a bone-chilling 20.2 K (−252.9 °C or −423.2 °F). Solid hydrogen doesn’t appear higher than 14.0 K (−259.2 °C or −434.5 °F). Such extreme temperatures are challenging to achieve in laboratory experiments (an understatement) and don’t occur inside the relatively warm interiors of Jupiter and Saturn. In order to create metallic hydrogen, extremely high pressures are needed.
Various experiments using everything from light-gas guns to the so-called “Z Machine” have attempted, and sometimes controversially claimed to create, high-pressure metallic hydrogen. Jupiter and Saturn, on the other hand, remain unconcerned about the petty squabbles of experimentalists. They’ve already created more metallic hydrogen than a high-pressure physicist could ever dream of.
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