Archive for the ‘Exoplanets’ Category

Superlative Chapter 2: The Fastest…

Thursday, July 31st, 2014

In the first edition of the Superlative series, we looked at the biggest things in the universe. Today we’ll explore another extreme – the fastest objects known.

Fastest Galaxy

The question of the fastest moving galaxy relative to us is not an easy one to answer. Because of the expanding universe, the speed at which distant galaxies are receding from our location is mostly due to the actual stretching of space. Thus, the further the galaxy from us, the further it is moving away from us.

Currently, the fastest known celestial object moving away from us is the primordial galaxy known as UDFy-38135539. It is also the furthest galaxy we have ever observed, at approximately 13.1 billion light years. This means UDFy-38135539 formed in the first 700 million years of the universe’s existence.

Infrared glow from the bow shock

Fastest Star

Recently, a number of new hypervelocity stars have been discovered in the Milky Way. These are stars that travel at more than two million miles per hour. The fastest of which is the star known as Kappa Cassiopeiae. It is traveling at 2.5 million miles an hour, and is at a distance of about 4000 light years from earth. Not to worry, Even if Kappa Cassiopeiae, which exists in the Cassiopeiae constellation, were heading directly for Earth, it still would take approximately 1.1 million years to reach our solar system.

Interestingly, hypervelocity stars such as Kappa Cassiopeiae impact the space in front of their direction of travel so much, that the interaction between the star’s magnetic field and the matter in space creates a large infrared glow. This phenomenon is known as a bow shock, and it can affect space up to four light years ahead of the star itself.

Artist’s rendition of VFTS 102

Fastest Rotating Object

The fastest rotating celestial body discovered to date does not exist in the Milky way, but rather a smaller galaxy approximately 160,000 light years away, known as the Large Magellanic Cloud. This star, known as VFTS 102, is about 25 times more massive than the sun, and was thought to be ejected from a binary star system. At its surface, it rotates at approximately 1 million miles an hour; about 100 times faster than our sun.

Fastest Planets

The fastest moving planet in our own solar system is Mercury. It has an orbital period (year) of just 88 Earth days, and moves through space relative to the sun at 107,700 mph. This is nearly double the 67,100 mph the Earth averages in it’s orbit around the sun.

As in most cases, exoplanets are far more extreme than our own solar system. Kepler 70b, for instance, has an orbital period of only 5.76 hours, giving it an orbital velocity of more than 375,000 mph.

Artist’s rendition of the Solar Probe Plus, set to launch in 2018

Fastest unmanned object

The current fastest man made object to exist was the Helios II probe launched on January 15th, 1976. It was put into orbit around the sun just inside the orbit of Mercury. At it’s nearest point (known as perihelion), it recorded a top speed of 157,078 miles per hour.

In the near future, the Juno probe which is set to visit Jupiter, will accelerate to 165,000 mph by using Earth’s gravity. Additionally, the Solar Probe Plus, set to launch in 2018, will take it on a similar mission as the Helios probe to study the sun. The probe is expected to reach speeds in excess of 450,000 mph, nearly three times the current record.

Fastest manned object

The fastest manned spacecraft, and thus the fastest humans have ever traveled relative to the Earth, was the Apollo 10 command module, on May 26th, 1969. This spacecraft was used for final testing in lunar orbit before Apollo 11 landed on the Moon. On its return flight home, it achieved a speed of 24,791 mph.

Exoplanets Pt. 2

Thursday, November 14th, 2013

This post is a part of a series on Exoplanets.

It doesn’t take long for us, once we discover our galaxy harbors approximately 160 billion exoplanets, to wonder how many could potentially support life. To answer that question, we need to analyze what we think is necessary for a planet to be habitable.

Liquid Water

Habitable zone for different stars

First and foremost, we think there needs to be some amount of water in liquid form on or beneath the surface of the planet. While complex organisms could utilize another molecule for life, such as methane, life as we know it exists almost anywhere there is liquid water.
In order for a planet to have liquid water on its surface, it needs to exist in what is known as the “habitable zone” (sometimes referred to as the Goldilocks zone). This zone defines the distance a planet must be from its star in order to maintain temperatures between 0° C and 100° C (freezing and boiling points of water). This zone is different for each star, based on the size and temperature of the star. The Earth, for example, exists on the inner edge of the sun’s habitable zone, while Mars exists on the outer edge.

“Rocky” composition

In order to support surface water, a planet must be primarily terrestrial, or made up of hard material like the earth. We have discovered many exoplanets within a star’s habitable zone that are speculated to be gas giants like Jupiter and Saturn.

Orbit

Things start getting a little bit more speculative when we consider what type of planetary motion is required for habitable life. For instance, we believe an exoplanet must have a relatively circular orbit around its parent star in order to remain within the habitable zone. If the planet’s orbit is much more elliptical, it will freeze and evaporate the water on the planet with every revolution around its star. Data collected so far suggests that 90% of all exoplanets have an orbit that is too elongated to support life.

Additionally, we surmise a habitable exoplanet must have some sort of rotation around an axis as it revolves around its star. If the planet does not rotate (it is tidally locked), the side facing the star will be extremely warm, while the dark side will have extremely low temperatures.

Mass

Along with composition, mass is another planetary characteristic scientists believe is crucial to successfully harboring life. If a planet is too small, its gravity will be unable to support an atmosphere which is believed to be crucial for complex life to form. Additionally, smaller planets lack the geological activity also thought to be necessary for life, such as plate tectonics which provide the necessary carbon dioxide into the air to build an atmosphere.

If a planet is too large, its composition will most likely be that of a gas giant, like Jupiter, or an ice giant, like Neptune. Currently we think Earth is at the lower end of the range of habitable planet masses, with some estimates stating a planet ten times the size of our Earth still could be habitable.

Moon?

Some scientists speculate some sort of satellite like our moon is required to sustain life. This is because it plays an important part in stabilizing the tilt of a planet. A chaotic tilt would wreak havoc on the planets climate.

Simple vs. Complex Life

An important detail of the search for life bearing exoplanets is defining exactly what life is. On Earth, life formed approximately 450 million years after the earth did. It did so in the form of simple single-celled organisms. It took another 3.5 billion years for multi-cellular, complex life to evolve. What this indicates is that while it requires a relatively short period of time for life to form, it takes significantly longer for it to form what we would consider today to be “animals”.

Much of the criteria above apply primarily to single celled life. There are additional factors to take into account when searching for complex and intelligent life. We will explore these additional factors, as well as the likelihood of finding intelligent life in the universe in one of our upcoming posts.

 

Exoplanets Pt. 1

Thursday, November 14th, 2013

Exoplanets

Since humanity first started gazing up at the heavens, we have wondered if we were alone in the universe. With Copernicus’ discovery that the Earth was just one of many planets orbiting the sun, we began to ask the question if our solar system was unique.

Our solar system currently has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune (If you’re wondering where Pluto went, we’ll be visiting its rise and fall in an upcoming post). Up until 1992 we were unsure as to whether any other planets existed in the visible universe. With the discovery of the first planet around the pulsar star PSR1829-10, that question was answered.

Numerous teams are currently searching for these planets outside of our solar system, known as exoplanets. As of this post, we have discovered approximately 854 exoplanets. Additionally, there are no less than 2,700 additional candidates that require further observation, but scientists expect at least 80% of those will be confirmed eventually.

How do we find Exoplanets?

There are many methods scientists have used to detect exoplanets. Here’s a brief overview of some of the more popular methods:

Radial Velocity: This method uses Doppler Spectroscopy to determine small changes in a stars position as a planet orbits it.

Because of Newton’s third law, the gravity exerted on the planet by the star to keep it in orbit is equal to the gravity exerted on the star by the planet. Thus, as the planet orbits, it “pulls” on the star slightly, which causes it to wobble.

In the same way a train’s horn sounds higher as it approaches and lower as it recedes, so too is light squished and stretched as an object moves towards and away from us. We can measure this movement down to less than 1 meter per second with modern instruments. From this “wobble”, we can determine the orbital period (the time it takes for the planet to orbit the star), and estimate the mass of the planet.

Pulsar Timing: This method utilizes pulsars- very dense stars that rotate quickly and emit radio waves at an extremely regular rate. Tiny fluctuations of this rate indicate the “wobble” also used in the Radial Velocity method. This method is notable for two reasons: It can detect very small exoplanets (down to 1/10th the size of the Earth), and it was the first method used to discover an exoplanet.

Transit Method: This is perhaps the most comprehensive method we have of discovering exoplanets. Since we cannot see them directly (exoplanets do not emit their own light), it is hard for us to determine the actual size of an exoplanet. The Transit method solves this issue.

Exoplanet Transient Method

The concept is relatively simple: as a planet passes in front of a star, the light from the star will dim slightly, as a small portion of it will be blocked by the orbiting planet. We can measure this dip in the overall brightness of the star to determine exactly how big the planet is. This also can give us the orbital period.

Combined with the Radial method, we can determine a planets density, and speculate as to its composition. Less dense planets may be made primarily of gas like Jupiter or Saturn, while denser planets may be rocky like the inner planets of our solar system such as Earth or Mars.

The Kepler Mission

To date, the most successful mission to find exoplanets is the Kepler Mission. Kepler is a large optical telescope currently in orbit around the Earth. Putting telescopes in space is beneficial because it removes the problem of the atmosphere distorting light as it travels to earth. It also solves the issue of inclement weather which can often hinder Earth-based observation.

Kepler utilizes the Transit method to look for tiny fluctuations in the stars light within its field of view. The telescope is currently pointing to a small area of the sky near the Cygnus constellation, and can monitor thousands of stars at once. To date, Kepler has discovered hundreds of exoplanets, with thousands more currently considered planetary candidates.

How many planets are there?

Perhaps one of the greatest things Kepler has revealed is the sheer number of planets orbiting other stars. The most recent estimates suggest there is on average 1.6 planets for each star in our galaxy. That means when you look up at the sky at night, roughly every speck of light you see has at least one planet orbiting it. What is even more amazing is that there are approximately 100 billion stars in the Milky Way galaxy, which results in about 160 billion planets.

In the next article we’ll discuss what it would take to sustain life one of these far away planets.