Colluqium November 15

On November 15, 2012 the University of Michigan welcomed Dennis Bodewits to speak on comets and asteroids.

Dennis Bodewits is an assistant research scientist in the Astronomy Department at the University of Maryland.  "His research emphasizes comets and asteroids, and he is a member of the EPOXI/Deep Impact and Stardust-Next science teams. His observational studies encompass X-ray, UV and visible regions, and makes use of mostly space-born telescopes, such as Swift, Chandra, and XMM-Newton".(http://www.astro.umd.edu/people/dennis.html)

In his speech Bodewits focused on the roles comets and asteroids played in the creation of water on Earth.  He had videos and many photos of artistic interpretations of water formation of Earth. Bodewits also gave detailed explanations of the compositions of asteroids and comets.

For more information on comets here is a link: http://www.michastrostudent.blogspot.com/2012/11/comets.html. For more information on asteroids here is a link: http://www.michastrostudent.blogspot.com/2012/11/asteroids.html. For more information on water formation on Earth here is a link: http://www.michastrostudent.blogspot.com/2012/11/the-water-of-earth-contribution-of.html.

The Water of Earth. The Contribution of Asteroids, Comets, and Meteors

Earth is a fascinating and amazing planet to study because it has surface water. Surface water is an extremely valuable resource. It is arguably the most valuable resource on Earth because it is essential to all living organisms and it formed over a large amount of time. Water formed on Earth through a process that lasted millions of years. 

The process that allowed water to form on Earth included; asteroids, comets, and meteors. Astronomers have many theories about this process. Some astronomers have different beliefs about the ratio of comets, meteors, and asteroids that were involved in the formation of water on Earth. All of the different theories that involve the different ratios and time scales can all be justified because no one really knows how water formed on the surface of the Earth. It is impossible to know because humans had not even been created when water formed on Earth. However, astronomers know that asteroids, meteors, and comets played a role in water formation on the surface of earth because the water had to have come from some outside source. 

Asteroids, comets, and meteors are very important celestial bodies that have been found in our solar system. Most importantly asteroids, comets, and meteors, contributed to water formation on the surface of the Earth. These celestial bodies, any natural body outside of the solar system, have been studied for many years and they are all very different from one another. Their differences make them very interesting. 

Asteroids are airless objects, most commonly found in the asteroid belt. The asteroid belt is located Mars and Jupiter. For more information on asteroids here is a link http://www.michastrostudent.blogspot.com/2012/11/asteroids.html

Comets are icy objects, most commonly found in the Oort cloud. The Oort cloud is a spherical cloud located 50,000 AU from the Sun. For more information on comets here is a link http://www.michastrostudent.blogspot.com/2012/11/comets.html

Meteors are dust to bolder sized particles of debris that are found in the solar system. 

Meteorites that astronomers have studied on Earth have hydrogen isotope ratios that help explain how elements like hydrogen and nitrogen got on the Earth. 

The biggest question astronomers are trying to answer is how volatiles like hydrogen, nitrogen, and carbon first arrived on Earth. Astronomers mostly believe that these elements arrived on Earth through collisions with comets and asteroids. One of the most accepted theories on how water formed on Earth suggests that during the creation of the solar system Jupiter and Saturn's orbits were disturbed and that caused comets in the outer solar system to move inward and later make their way towards Earth. These comets collided with Earth and left ice and other elements behind. Later when an asteroid collided with the Earth, the ice was melted and liquid water was then formed on the surface of the Earth. This process, according to astronomers, happened many times and it took millions of years.

Comets

Comets are known as “dirty snowballs,” because they consist of a mixture of ices (both of water and frozen gases), carbon dioxide, ammonia, methane, and dust. The core of a comet is solid and it consists of ice and dust.

Comets also have two tails. The first tail is an ion tail. The ion tail is blue because it consists of ionized CO+ and it scatters blue light. The second tail is the dust tail. The dust tail is green and consists of the dust that is pushed off of the comet and reflects radiation from other sources. The tails of a comet can reach 160 million kilometer long. 

 

The average comet has a mass of 10^14 kg, a diameter of 20 km, a density of 0.6 g/cm^3, and an albedo of .05.

Comets are mostly located in the Oort cloud, except for the occasional comets that streaks through the inner solar system. The Oort cloud holds millions and millions of comets and the Oort cloud is found much farther out than the orbit of Pluto. It is generally believed that we got our water when comets collided with the Earth.

Asteroids

Asteroids are marvelous celestial objects, not only because they played a huge role in water formation on Earth through various collisions with Earth's surface, but because they are so complex. Asteroids are irregularly shaped, rocky objects that usually are considered small objects or minor planets. They are rocky fragments that were left over from 4.6 billion years ago when the solar system formed. 

 The average asteroid is very complex because it has a diameter of 20 km, a density of 0.3 g/cm^3, and an albedo of less than .05. They also have an average surface temperature of 100 degrees Fahrenheit. 

 Asteroids are also very interesting because they fall into three different categories based on their compositions; C-type (carbonaceous) asteroids, S-type (sillicaceous) asteroids, and M-type (metallic) asteroids. C-type asteroids are greyish and are the most common asteroids. They make up 75 percent of all known asteroids in the solar system. S-type asteroids are reddish and greenish in color and they make up 17 percent of all known asteroids. M-type asteroids are red in color, consist of mostly nickle, and are located mostly in the middle of the asteroid belt. 

 Asteroids orbit the Sun in elliptical orbits in the asteroid belt that is located between Mars and Jupiter. The asteroid belt is made up of many different sized asteroids. The asteroid belt holds more than a million asteroids, of which 200 are larger than 60 km in diameter and 750,000 are larger than 1 kilometer in diameter. Half of the mass that is found in the asteroid belt comes from the four largest asteroids. The four largest asteroids are Ceres, Vesta, Pallas, and Hygiea. 

 The total mass of all the asteroids in the solar system is less than the mass of the Moon, but asteroids are still very dangerous. Many asteroids collided with the Earth in the past. The asteroids that collided with the Earth, depending on their sizes, caused great amounts of damage. Therefore many astronomers study the orbital paths of asteroids and believe that these earlier collisions, together with earlier comet collisions, contributed to water formation on Earth's surface.

Colloquia November 8

On November 8, 2012 the University of Michigan welcomed back a former graduate student Zhaohuan Zhu. 

Zhaohuan Zhu was a graduate student at the University of Michigan some years ago. He now students at Princeton.

Zhu focused of the fluid dynamics of planetary system formations. He described why he believed it was better to used 3D over 2D simulations. He said it was better because we could see more data about the way a planetary system works.

He went into great detail about how planets form. He talked about using radio velocities techniques (measuring the wobble of the planet) and imaging (viewing the planet head on).

Zhu also showed a very interesting video about the Almer telescope and its array formation. It is composed of many radio telescopes to give astronomers a deeper clearer view of the universe.With the Almer telescope astronomers will be able to view deeper into space as far back as many radio waves, and since they are in an array they are not limited by the viewing power of the telescope itself. They are all put together as one so essentially the viewing power is only limited by the amount of telescopes in the array.

Planetary System Formations

Planetary System Formations

To understand how planetary systems form I will focus on the Solar system because it is the most widely studied system. Astronomers believe the nebular hypothesis when it comes to the solar system. They believe that the solar system formed from the collapse (gravitationally) of a portion of a very big molecular cloud. The formation of the Solar system occurred about 4.55 billion years ago

The molecular cloud was most likely about 20 pc and the part that actually collapsed to form the solar system was about 1 pc or 20,000 AU in size. 

Here is a picture of a molecular cloud:

The 1 pc region included a mass of a little bit more than the Sun (around 1.98*10^30 kilograms). Hints: the sun is the most massive object in the Solar system. This region was composed of primarily Hydrogen and Helium with very tiny amounts of lithium.

The molecular cloud at a certain point began to spin very fast because of angular momentum. The atoms inside cloud began to collide and they converted their kinetic energy into heat. As it continued to collapse the center of it was much hotter than is surrounding disk. After about 100,000 years the forces of gas pressure and gravity competing led to the formation of a protostar . After 50 million years the protostar became hot enough to fuel itself through nuclear fusion and the protostar became what is known as the Sun.

The planets in the solar system formed from the disc shaped cloud containing dust and gas that the sun left after its formation. Astronomers believe that the planets (like the earth) began as grains of dust and accumulated matter over years until they became planets. This process is very inefficient according to Astronomers when compared to star formation. While the gas giants in the solar system formed much farther out.

What is a Planetary System?

Astronomers have studied the Solar system for many years and because of this they know that planetary systems take 1 to 10 million years to form.

Here is a general picture of what a planetary system could looks like:

A planetary system is a collection of gravitationally bound celestial objects that orbit around a star or a system of stars.  These systems vary in sizes and vary in the amount of planets they contain.  Astronomers have frequently discovered single planetary systems using radial velocity method calculations.

Planetary systems usually describe systems with one or two planets and a star, but these systems can contain multiple stars, multiple planets, satellites, dwarf planets, asteroids, meteoroids, and comets.

Astronomy Colloquia 11/1

On November 1, 2012 the Astronomy department at the University of Michigan held a Colloquia. Jason Wright, an assistant professor of astronomy and astrophysics at Pennsylvania State University, was the main speaker.

Wright is a member of the Center of Exoplanets for Habitable Worlds and the Penn State Astrobiology Research Center (part of the NASA Astrobiology Institute). He study stars, their atmospheres, their activity and their planets.

During his speech he focused on the detection and the discovery of exoplanets.  Exoplanets are planets that are discovered outside of the solar system. for more info on exoplanets go here: http://www.michastrostudent.blogspot.com/2012/11/exoplanets.html. His speech was very interesting because it described the indirect (for more information:http://www.michastrostudent.blogspot.com/2012/11/indirect-exoplanet-detection.html)  and direct (for more information: http://www.michastrostudent.blogspot.com/2012/11/direct-exoplanet-detection.html) methods of detecting exoplanets in detail.  He also described how hard it is to detect a habitable planet and the key components that define an exoplanet as habitable or non habitable. 

Direct Exoplanet Detection

There are two methods used to directly detect exoplanets.

The first direct method used is referred to as imaging. Planets are light sources, although sometimes very faint light sources. To discover exoplanets using this method observers can see light produced by an exoplanet. Using this method is extremely difficult because older or middle aged exoplanets produce very little light, especially if they are small. This method has usually only worked when observing hot young exoplanets. The light produced by the exoplanets' companion star can literally out shine the light produced by the exoplanet and the exoplanet can go undetected. 

 

The second direct method is infrared interferometry. Traditionally telescope's viewing power is limited by the diameter of the telescope's mirror or lens, but combining telescopes in an array can greatly boost a telescopes viewing power. Array telescope in space can then use infrared interferometry to detect exoplanets and their companion stars. This method is the newest method of detecting exoplanets but it seems to be the most promising because array telescopes could potentially easily detect exoplanets that take years to detect using other methods.

Indirect Exoplanet detection

 There are four indirect methods used to detect exoplanets.

The first method indirect is the radial velocity method. It is the most common method used to discover exoplanets. The reflex motion of a star due to the orbiting planet is measures as a change in a stars radial velocity. The radial reflex of the star is compared to the exoplanets orbit, using the measurements of Doppler shifts. These comparisons are used to calculate the mass of the exoplanet, its orbits shape, and its orbital distance. The exoplanets discovered using this method tend to be very low mass planets. 

 The second indirect method is the astrometry method. This method measures a star's position and how it changes over time so is mostly used to discover exoplanets that have very long periods.  After that you can use the acquired information to determine the actual mass of the exoplanet because you can determine the orbital plane of the exoplanet. The best place to use astrometry is in space but you can use this method from the surface of earth. The exoplanets discovered using this method tend to be very far from the solar system. 

 

The third indirect method is the transit method. A transit is an event that occurs when a celestial object moves in-front of another celestial object. When the celestial body moves infront of the other larger celestial body it hides a small portion of it. Observers can see this occurrence at particular orbital points. This method reveals exoplanets when they transit their larger companion stars. Observers see a drop in the visual brightness of the companion star. The exoplanets orbit has to be perfectly aligned with the observers viewing point or the observer could easily miss the exoplanet. Also there is a very high amount of false exoplanet detections when using the transit method because dust, gas, and even planetary debris can easily cause a star to appear dimmer. 

The fourth indirect method is gravitational lensing. Gravitational lensing occurs when the presence of matter effects the path of a light ray. The light ray, from the observers view can appear to be curved or highly unusual. The gravity field of a star can behave like a lens and it can magnify the light of a background star. The star, the background star, and the Earth all move relative to each other. If the lensing star has a companion exoplanet, then the exoplanet's gravitational field can be detected through its contribution to lensing effect. This effect only occurs when the stars are almost perfectly aligned. The lensing events are very short and they can never be repeated so it is very difficult to detect exoplanets using this method.

Exoplanets

An exoplanet is a planet that is found outside of the solar system.  Exoplanets are also referred to as extrasolar planets.

Astronomers use many different techniques to locate these planets. Astronomers have discovered 843 exoplanets, 663 are in single planetary systems and there are 126 exoplanets in multiple planetary systems. Astronomers have predicted that there are above a billion exoplanets in the Milky Way galaxy.

Below is an example of an exoplanet orbiting in a binary star system:

To discover exoplanets astronomers use three techniques. The first technique involves using precise radial velocities, and this technique is the most commonly used. The second technique is the transit method, and the third is imaging.  Imaging is the hardest method of discovering exoplanets used be astronomers.


Here is a picture of some of the discovered exoplanets compared to their companion stars: