Ryan Spielvogel

Adam Whitener

Iota Draconis

(HD 137759)

Where to find on sky/constellation

It is in the Northern sky, near the constellation Ursa Minor. It is in the constellation Draconis (it is the fourth star in the tail of Draco).

Luminosity

We were not told the luminosity of our star directly. We had to calculate it using information given.

Luminosity of the star (L_star) = L_sun * 2.512 ^{(M,sun – M,star)}

The problem with this is that we were not given the absolute magnitude of the star (M_star)

So first, we had to find the absolute magnitude of the star using the equation:

Absolute Magnitude (M_star) = m_star – 5*log (d_star) + 5

Where m_star is the apparent magnitude of the star from Earth, and d_star is the distance from Earth to our star.

Thankfully, we were given the apparent magnitude of our star, its distance from Earth, the absolute magnitude of the Sun and the luminosity of the Sun. So we can now calculate the luminosity of the star.

m_star = 3.3

d_star = 31.5 pc

M_sun = 4.72

L_sun = 3.9 x 10²⁶ W

M_star = 3.3 – 5*log(31.5) + 5 = 0.808

L_star = (3.9 x 10²⁶ W)(2.512^{(4.72 – 0.808)}) = 1.406 x 10²⁸ W

Albedo

The Albedo of a planet is the percentage of its star’s light that is reflected off of its surface and/or atmosphere. This number can range from (0, 1). Since we do not have any way of knowing what the albedo of our planet is, we picked three albedos, a high, a low, and a mid, to obtain a range of temperatures for our planet

How do we get the temperature of our planet?

We have an equation that relates the temperature of the planet to the luminosity of its star, the distance of the planet to its star and the planet’s albedo. This equation is:

T =

Finding the Temperature of our planet.

The albedos that we used were 0.05, 0.35 and 0.6. Using these albedos, we obtained the temperatures given below.

T_0.05 = = 584.4 K

T_0.35 = = 531.5 K

T_0.6 = = 470.7 K

What could the composition of our planet be?

Certain elements and compounds condense when the temperature is cold enough. Here is the chart for when silicates, metals, water, ammonia, and hydrogen and helium condense.

Silicates	1200 – 1800 K
Metals	500 – 1000 K
H2O, NH3, CH4	120 – 270 K
Hydrogen	20 K
Helium	----

Our planet is most likely composed of many different metals. These could be metals like iron, nickel, copper and zinc. The planet will not have liquid water or ammonia or methane, as the temperature is much too high for those substances to stay in liquid form.

This is, of course, assuming that our planet was formed at its current temperature. This might not be so if the planet has migrated.

Could our planet have migrated?

Our planet could very well have migrated. This is a possibility because the planet is the mass of eight and a half Jupiters. However, the planet is only 1.34 au away from its star. Whenever a planet is close to a star, there is not much dust and/or materials for the planet to form. So, because the planet is that large, it must have formed farther away from the sun and migrated in to where it is now.

Planet migration – temp. now vs. formed

The temperature now is surely hotter than what it was when the planet was formed. This is because the planet was so far out when it formed that it’s star would not have given nearly as much heat to the planet as it does now that the planet has migrated in close to the star.

Discussion of possibility of life

It does not seem that there is a possibility for life. The planet is much hotter than Earth, even with a high albedo, so it would be very hard for amino acids and proteins to develop there. This is a problem because with a lower albedo the temperature gets even higher, and life has a better chance of developing on a planet that has high cloud-cover (high albedo). Also a low albedo indicates that the planet has very little or no atmosphere, so the organisms would most assuredly die quickly, as they would not have anything to breathe nor anything to block out the lethal UV radiation of their star.