An Investigation of HD52265: Andrew Hardin and Ryan Outlaw

Introduction

            As part of our Miniterm course (The Search for the Origins of Life), we selected a known planetary start system to investigate the properties of the said planets.  From a list of the approximately eighty known planets, we chose a star whose properties we such that we would be able to view the star readily (these properties are detailed below).  For our analysis, we selected the planetary star system HD52265.  From known information about the star and its planet, we calculated several properties of the planet to help us in our analysis of it.  The analysis and our conclusions about our planet are detailed in the following document.

 

Star and Planetary Properties

            In order to calculate the temperature of our star, we had to know certain properties of the star and the planet.  These properties are listed below:

 

Right Ascension

Declination

Apparent Magnitude

Spectral Type

Absolute Magnitude

7h 0m 18s

-5° 22’ 2”

4.08

G0V

4.5

Jupiter Mass

Period (years)

Distance from Earth

Eccentricity

Semimajor Axis (AU)

1.13

0.3258

27.8pc

0.29

0.49

 

We were able to use these values to calculate information about our star and our planet.  In order to calculate the luminosity of our star, we used the following equation:

M is the absolute magnitude of the star.  The value  is the luminosity (in watts) of our star.  The absolute magnitude of the star must be found using the spectral type of the star.  The diagram show here is used to find the absolute magnitude of the star.  By finding the spectral type (G0) and then following it to the V-line, we can find both the absolute magnitude (on the right, approximately 4.5), the luminosity of the star, and its surface temperature.  The red lines show the connection between the spectral type and the absolute magnitude of the star.  Since our absolute magnitude is approximately 4.5, we used this value for M.  Thus, our star’s luminosity is  watts.

            Using this luminosity value, we can find the temperature of our planet.  The equation for temperature is as follows:

L is the luminosity of the star, A is the albedo of the planet, s is a constant ( Wm-2K-4) and d is the planet’s distance from its star (Semimajor axis, in kilometers).  Albedo is a measure of the planet’s tendency to reflect light from its star due to the presence of clouds, ice, water, and land.  Since we have no way of detecting the presence of these factors, we used a range of albedo values (A={0.1, 0.3, 0.5} that are seen in our solar system.  From this, our temperature values are as follows:

 

Error in Temperature Calculation

            As with any calculation where only limited variables are known (thus only limited information is used for the calculation), there is error.  We, of course, cannot calculate this error.  However, we can predict possible sources of error based on sources of error for planets in our solar system.  Most of the planets in our solar system have actual temperatures similar to those calculated using the formula referenced above.  Venus, however, has a calculated temperature much lower (approximately 500K lower) than its actual temperature.  This can be explained because of the atmospheric composition.  The atmosphere of Venus contains many greenhouse gases that absorb the infrared radiation released on the surface of Venus (as a result of the visible light from the sun).  This trapped radiation exerts itself in the form of heat, thus further heating the planet.  In addition to the greenhouse effect, gravitational energy (in the form of kinetic energy) from accretion increases the temperature.  One additional source of heat not accounted for in the aforementioned equation is heat from radioactive decay.  In our solar system, the main source of error comes from the greenhouse effect.

            Likewise, our planet may be experiencing similar effects.  While we cannot know with certainty about the existence of greenhouse gases or radioactive decay, we can say with relative certainty that additional heat not accounted for is probably not a result of kinetic energy due to accretion (being that our planet has probably exceeded its infancy).  We cannot be certain of error, therefore, and can only guess that our estimated temperatures are off by some degree, hopefully less than 50K of difference.

 

Location in the Sky

            Having selected a star whose properties are such that we could view the star at the appropriate time (approximately 9:00pm), it is important to know where to find HD52265.  Our star is located on the northern most point of Canis Major.  The star is part of a smaller portion of the constellation, located on the tip of a scalene triangle.  To help locate this region of the sky, we simply found Sirius, the brightest star in the sky (with an apparent magnitude of –1).  After finding Sirius, HD52265 was located north-northeast of Sirius.  The star chart details the location of our star (please refer to the table on above for the right ascension and declination).

 

Composition and Possibility of Life

            The temperature of our planet is indicative of an earth-type planet.  However, calculations of mass indicate that it is 1.13 times more massive than Jupiter.  This leads us to believe that the planet, during accretion, we initially much farther out than it currently is, due to its relative mass.  Evidence suggests that during accretion, the planet was cool enough to condense silicates, metals and ices (such as water, NH3 and CH4).  This means that the planet has migrated.  Its current distance from its star (0.49au) would mean that at the time of accretion there would be too much heat to form such a massive planet comprised of metals and ices.  Therefore, the planet probably formed at a distance similar to Jupiter’s current distance and has now migrated towards its star.

            Based on this speculation, we do not feel that it is very likely that this planet harbors life.  The immense size (and probably immense gravity) and composition of ices, metals and silicates would probably lend the planet to being a totally liquid planet, like Jupiter, whose short distance from its star would surely not be a probable location for even the most resilient extremophiles.  Therefore, we do not feel as though HD52265 contains life.

 

Conclusions

            Based on our research on this planet, we do not feel that its properties, both known and calculated, would be a probable location of life due to its composition and location relative to its star.  However, since we cannot be entirely certain, we cannot rule this planet out as being an important focus of study in the future.