website to check
new Earth's like planet found
We can not see a exo planet orbiting a star by using a telescope. The planet is too close to the star and
we can't distinguish them. The angular is too small and the distortion by the Earth atmosphere and/or telescope is
too large. For example the photo below show a binary star system. Sirius A (large) and Sirius B. Because the distortion
it would have been impossible to see a planet orbiting Sirius.
We need to use another method. A planet and a star orbit their center of mass and the following equation is true:
DsMs = DpMp Ds is the distance from star to center of mass, Dp is the distance from planet to center of mass.
Ms is the mass of the star. Mp is the mass of the planet.
Newton's third law = They both " feel" the same gravitational pull which means the total momentum of the system is conserved.
Ms Vs = Mp Vp
If the Planet has a large velocity (up on the drawing) the the star has a small velocity in the opposite direction (down on the drawing).
We can detect the small velocity of the star and this how we know about a planet we can't see.
more on this website
example1: Find the speed of the around around the Sun in m/s
with d = 2pi a and s = d/t, t = 1 year, a = 1AU
example2: How fast is the Sun moving in response of the planets.
hint: its motion is induced mainly by Jupiter. so take only Jupiter into account.
use: Ms Vs = Mj Vj , Mj=2 1027 kg and Ms = 2 1030 kg
It makes sense that the Sun is moving 1000 times slower than Jupiter since it is 1000 times more massive.
This speed can be detectable. so re can detect Jupiter's like planet.
example3: let's now compute the motion of the Sun as induced by the EArth.
Vs = VE ME/Ms =.... convert into cm/s
This is not yet detectable with our instruments.
To detect a planet (jupiter type) around the star we need to use its Doppler shift.
If the star moves on a circular orbit away from us and toward us the Doppler shift
will increase and decrease in a periodic way. (see chapter on Doppler shift)
The velocity versus time is a sine wave if the orbit is circular. (see example below)
The relative radial speed can be computed using the formula : (L-Lo)/L = VR/c
Lo is the wavelength (color ) of the star if it were at rest (or moving sideway).
L is the observed wavelength, VR is the radial velocity (0 if star is moving side way)
c is the speed of light.
great square of Pegasus (see google Earth to locate the star). They plotted the radial velocity versus time :
ALong the x-axis you can read the orbital period of the planet ; only 4days !!
convert in earth years . p = ________ years.
Use kepler law to find the semi major axis a = _______ AUs. Suppose the star is 1 solar mass M = Mo
hint: suppose M = 1 solar mass. a3 = p2 M a in earth years, p in AUs , M in Mo, Mo the mass of the Sun
This planet is very close to the star and this is not expected. We expect the Jupiter like planets to form farther away
where it is not that hot so gas and ice can stick together. The planet didn't form the same way our jovian planets did.
You can find the speed of the planet using the formula : Vp = 2 pi a / p . you need to convert p in seconds and a in meters.
(1AU = 1.5 1011 meters and 1 year = 3 107 seconds). Compute Vp.
This is very fast. It has to be so the planet can stay into orbit to resist gravity.
note: the planet and the star orbit the center of mass. they are across from each other like attached to the same seesaw.
see this applet. (made for binary star but same idea)
The y-axis gives you the speed of the star about Vs = 50m/s
Using Vs and Vp compute Mp.
(hint: Mp = Ms Vs/Vp )
This is 1/3 the mass of Jupiter. This is very massive planet (more massive than Saturn). The presence of this so called " hot Jupiter"
so close to a star contradict our planetary formation theory. Since then, more exoplanets have been found.
Some stars have up to 3 planets. The sine curve has wiggles into it in that case.
more on this case
Scientists have developped another way to identify exoplanets. This other method works only when the orbit is edge on.
This method is called transits. It is the dip of light due to a planet passing in front of the star.
This method worked and was used to find " hot jupiters" in the center or ou milky way/.
Acientists learnt in their search that you won't find " hot jupiter" in a very dense cluster of stars.
stars tend to kick off planets from their orbits. Planets tend to form around stars with a high " metallicity"
= more elements that are not H or He. 16 exoplanets have been found in the center of of milky way using the transit method.
Someitines, you can't use the soppler shift method because the stars are too faint.
more on exoplanets
see here an animation if the orbits are not circular
more on the Math
new earth in formation
new Earth's like planet found
We can not see a exo planet orbiting a star by using a telescope. The planet is too close to the star and
we can't distinguish them. The angular is too small and the distortion by the Earth atmosphere and/or telescope is
too large. For example the photo below show a binary star system. Sirius A (large) and Sirius B. Because the distortion
it would have been impossible to see a planet orbiting Sirius.
We need to use another method. A planet and a star orbit their center of mass and the following equation is true:
DsMs = DpMp Ds is the distance from star to center of mass, Dp is the distance from planet to center of mass.
Ms is the mass of the star. Mp is the mass of the planet.
Newton's third law = They both " feel" the same gravitational pull which means the total momentum of the system is conserved.
Ms Vs = Mp Vp
If the Planet has a large velocity (up on the drawing) the the star has a small velocity in the opposite direction (down on the drawing).
We can detect the small velocity of the star and this how we know about a planet we can't see.
example1: Find the speed of the around around the Sun in m/s
with d = 2pi a and s = d/t, t = 1 year, a = 1AU
example2: How fast is the Sun moving in response of the planets.
hint: its motion is induced mainly by Jupiter. so take only Jupiter into account.
use: Ms Vs = Mj Vj , Mj=2 1027 kg and Ms = 2 1030 kg
It makes sense that the Sun is moving 1000 times slower than Jupiter since it is 1000 times more massive.
This speed can be detectable. so re can detect Jupiter's like planet.
example3: let's now compute the motion of the Sun as induced by the EArth.
Vs = VE ME/Ms =.... convert into cm/s
This is not yet detectable with our instruments.
To detect a planet (jupiter type) around the star we need to use its Doppler shift.
If the star moves on a circular orbit away from us and toward us the Doppler shift
will increase and decrease in a periodic way. (see chapter on Doppler shift)
The velocity versus time is a sine wave if the orbit is circular. (see example below)
The relative radial speed can be computed using the formula : (L-Lo)/L = VR/c
Lo is the wavelength (color ) of the star if it were at rest (or moving sideway).
L is the observed wavelength, VR is the radial velocity (0 if star is moving side way)
c is the speed of light.
Observing the radial velocity of the host star in an attempt to determine its reflex motion
as its perturbed by a massive planet. This technique is known as "Doppler wobble"
See this page for nice animation
In October 1995 astrophysicists found a jupiter's like planet around the star 51 Pegasus. This star is located in the sky next to thegreat square of Pegasus (see google Earth to locate the star). They plotted the radial velocity versus time :
ALong the x-axis you can read the orbital period of the planet ; only 4days !!
convert in earth years . p = ________ years.
Use kepler law to find the semi major axis a = _______ AUs. Suppose the star is 1 solar mass M = Mo
hint: suppose M = 1 solar mass. a3 = p2 M a in earth years, p in AUs , M in Mo, Mo the mass of the Sun
This planet is very close to the star and this is not expected. We expect the Jupiter like planets to form farther away
where it is not that hot so gas and ice can stick together. The planet didn't form the same way our jovian planets did.
You can find the speed of the planet using the formula : Vp = 2 pi a / p . you need to convert p in seconds and a in meters.
(1AU = 1.5 1011 meters and 1 year = 3 107 seconds). Compute Vp.
This is very fast. It has to be so the planet can stay into orbit to resist gravity.
note: the planet and the star orbit the center of mass. they are across from each other like attached to the same seesaw.
see this applet. (made for binary star but same idea)
The y-axis gives you the speed of the star about Vs = 50m/s
Using Vs and Vp compute Mp.
(hint: Mp = Ms Vs/Vp )
This is 1/3 the mass of Jupiter. This is very massive planet (more massive than Saturn). The presence of this so called " hot Jupiter"
so close to a star contradict our planetary formation theory. Since then, more exoplanets have been found.
Some stars have up to 3 planets. The sine curve has wiggles into it in that case.
Scientists have developped another way to identify exoplanets. This other method works only when the orbit is edge on.
This method is called transits. It is the dip of light due to a planet passing in front of the star.
This method worked and was used to find " hot jupiters" in the center or ou milky way/.
Acientists learnt in their search that you won't find " hot jupiter" in a very dense cluster of stars.
stars tend to kick off planets from their orbits. Planets tend to form around stars with a high " metallicity"
= more elements that are not H or He. 16 exoplanets have been found in the center of of milky way using the transit method.
Someitines, you can't use the soppler shift method because the stars are too faint.
more on exoplanets
see here an animation if the orbits are not circular
more on the Math
new earth in formation