a database of spectra, albedos, and colors of solar system ... · neptune to the left is the...

A Database of Spectra, Albedos, and Colors of Solar System Bodies for Exoplanet Comparison Jack Madden, and Lisa Kaltenegger

Cornell University - Carl Sagan Institute

Process mV = −2.5Log10

(∫

Vλfλdλ∫

Vλfλ,vegadλ

)

mV = −2.5Log10

(∫

Vλkfλ,normdλ∫

Vλfλ,vegadλ

)

k =(

∫

Vλfλ,vegadλ∫

Vλfλ,normdλ

)

10mV−2.5

p = 1φ(α)

d2a2bfλR2ba

2⊕fλ,Sun

0.5 1.0 1.5 2.0 2.5

10-5

10-4

10-3

10-2

10-1

100

101

λ (µm)

NormalizedFlux

Neptune The conversion process is best conveyed through an example. To the left is the normalized data published in 2009. Also published was the V magnitude of Neptune at 7.9. Using the Vega spectrum, filter responses, and equations to the right you find that this particular spectra needs to be multiplied by k=4.4x10-16 in order to obtain the proper V magnitude of 7.9.

0.5 1.0 1.5 2.0 2.510-21

10-20

10-19

10-18

10-17

10-16

10-15

λ (µm)

SpectralIrradiance(W

/m2 Å

)

Neptune To the left is the un-normalized result of the spectra we started with. From here we are now able to calculate the magnitudes in all bands to obtain colors. At this stage we can use the albedo equation to get the geometric albedo of the body as shown at the right. From the albedo, different stellar spectra can be used to find what the colors would be if this planet was orbiting that star.

0.5 1.0 1.5 2.0 2.50.0

0.2

0.4

0.6

0.8

1.0

λ (µm)

GeometricAlbedo

Neptune

For an enhanced experience scan

this poster with LAYAR

Conclusion This database of spectra, albedos, and colors provides a set of references for many future works in the identification and characterization of exoplanets. Similar features discovered in the spectra of exoplanets may also be studied within the solar system for greater understanding. All of the data we generated will be available for digital download through the Carl Sagan Institute for use in future exoplanet investigations.

This assemblage of data will make it easier to decipher the spectra of other worlds similar to

those found in our own solar system.

0.5 1.0 1.5 2.0 2.5

0.0

0.2

0.4

0.6

0.8

1.0

λ (µm)

GeometricAlbedo

Alien World

Outline With spectra of extrasolar planets becoming more common it is essential to have a complete and accurate set of solar system reference spectra for comparative planetology. Albedos and colors of solar system bodies can be used to distinguish planetary types (Cahoy 2010) and determine potential habitability (Traub 2003). Many of the most widely used spectra of solar system bodies are over 20 years old and comparing data sets can be difficult due to inconsistent wavelength range, instrument response, resolution, and data formats. We converted the Tohoku-Hiroshima-Nagoya planetary spectra library (Lundock et. al. 2009) of 18 solar system bodies to a database of spectra, albedos, and colors. Absolute geometric albedos also provide us with a method for obtaining the spectra of these bodies as if the Sun were replaced by another star.

Converted the spectra of 18 solar system bodies to assemble a database of spectra,

albedos, and colors for characterizing upcoming exoplanet discoveries.

Tools Below are the stellar spectra and the filter responses used to determine the conversion factors and colors of the bodies around the different star types. The Sun and Vega spectra are STIS CALSPEC spectra, the other stars are from the Castelli and Kurucz atlas, and Phoenix models. The Vega, and M9V spectra were multiplied by 1013 and 103 respectively to fit on the same plot. Filters are Johnson, Cousins, and Bessel filters. Mathematica was used for the computations and plotting.

�� -�

��-�

��-�

��-�

��-�

��-�

��

��

��

��

(�/�

��)

��

��

��

��

��

��

��

��

��

��

��

��

��

��

λ (µ�)

��

��

� � � � � ��

Filters Reference Stars

Shown here are the albedos of the solar system bodies calculated from the THN-PSL overlaid with previously published data. While most show a good fit others were found to be contaminated and unreliable. These are outlined in red and their alternatives were used in the analysis.

Below we assemble the colors the solar system bodies as if the Sun was replaced by a different star type. Each plot shows the positions of points around the Sun connected to the points around the new star to show displacement.

Acknowledgements We would like to thank Ramsey Lundock, Erich

Karkoschka, Paul Helfenstein, and the NY Space Grant Consortium for helpful input and support.

0.5 1.0 1.5 2.0 2.50.0

0.2

0.4

0.6

0.8

1.0

λ (µm)

GeometricAlbedo

Rhea

0.5 1.0 1.5 2.0 2.50.0

0.2

0.4

0.6

0.8

1.0

λ (µm)

GeometricAlbedo

Titan

0.5 1.0 1.5 2.0 2.50.0

0.2

0.4

0.6

0.8

1.0

λ (µm)

GeometricAlbedo

Uranus

Here we show how the surface types can be separated based on disk integrated color. From left to right we show the gas, rocky, and icy bodies. Above are color-color diagrams made from the spectra we obtained. Below are the spectra for each surface class overlaid with the color bands we examined in the color plots. These plots affirm that the surfaces of solar system bodies are distinguishable based on their reflected color. This means that if we find similar planets outside our solar system they too will be distinguishable on a color-color diagram.

▲

▲ ▲▲▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲■

■

■

■

■

■

●●

●

●●●

●

△

△△△△

△

△

△

△

△

△

△

△

△

△□

□

□

□

□

□

○○

○

○○○

○

-� -� -� -� � � � �-�

-�

-�

-�

-�

�

�

�

�-�

�-�

��-��

Sun F0V Type△ ▲ Gas□ ■ Ice○ ● Rock

Error

▲

▲▲▲▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲■

■

■

■

■

■

●●

●

●●●

●

△

△△△△

△

△

△

△

△

△

△

△

△

△□

□

□

□

□

□

○○

○

○○○

○

-� -� -� -� � � � �-�

-�

-�

-�

-�

�

�

�

�-�

�-�

��-��

Sun K0V Type△ ▲ Gas□ ■ Ice○ ● Rock

Error

▲

▲▲▲▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲■

■

■

■

■

■

●●

●

●●●

●

△

△△△△

△

△

△

△

△

△

△

△

△

△□

□

□

□

□

□

○○

○

○○○

○

-� -� � � �-�

-�

-�

-�

-�

�

�

�

�-�

�-�

��-��

Sun M0V Type△ ▲ Gas□ ■ Ice○ ● Rock

Error

▲

▲▲▲▲

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲■

■

■

■

■

■

●●

●

●●●

●

△

△△△△

△

△

△

△

△

△

△

△

△

△□

□

□

□

□

□

○○

○

○○○

○

-� -� � � � � �-�

-�

-�

-�

-�

�

�

�

�-�

�-�

��-��

Sun M9V Type△ ▲ Gas□ ■ Ice○ ● Rock

Error

M0V

K0V F0V

M9V

6 Madden et al.

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

��

λ (µ�)

��

��

��

��

��

Figure 5. aSpencer 1987, bReddy et al. 2015, cNoll et al. 1997, dKaltenegger et al. 2010, eMeadows 2006, fFanale et al. 1974, gKarkoschka1998, hLane & Irvine 1973, iMcCord & Westphal 1971, jMallama 2017, kFink & Larson 1979, lDouté et al. 1999, kPollack et al. 1978

MNRAS 000, 1–10 (2016)

Refs.

Result

Result Other Stars

Colors

Albedos Result

References and a digital version of this poster can be found online at astro.cornell.edu/~jmadden

▲

▲

▲

▲

▲

▲

▲

▲

▲

▲▲

▲▲▲▲

▲▲1

2

3

4

1

2

1

2

3

4

12

3

▲ ��▲ ��▲ ��▲ ��▲ ��▲ ��

��

-� -� -� -� � � � �-�

-�

-�

-�

-�

�

�

�

�-�

�-�

��

●● ●●●●

●●●●

●●

● ��● ��● ��● ��● ��● ��

��

-� -� -� -� � � � �-�

-�

-�

-�

-�

�

�

�

�-�

�-�

��

■■

■■■■

■■

■■■■

■ ��■ ��■ ��■ ��■ ��■ ��

��

-� -� -� -� � � � �-�

-�

-�

-�

-�

�

�

�

�-�

�-�

��

� � �

�� -�

��-�

��-�

��-�

��-�

��-�

��

��

λ (µ�)

��

��

� � �

�� -�

��-�

��-�

��

��

λ (µ�)

��

��

� � �

�� -�

��-�

��-�

��-�

��

��

λ (µ�)

��

��

Ice Rock Gas

a database of spectra, albedos, and colors of solar system ... · neptune to the left is the...

Documents