Andy's Wiki
Exoplanetary Scratchpad

[SysBP Img]

AC+27°28217 is best known as Gliese 436. The second known red dwarf planetary system. Contains one of the first Neptunians discovered and a few potential planets. The star is about half the sun's mass. It is over 11 Billion years old and may be a part of the old disk of the Milky Way. Planet b temporarily later found to be the smallest exoplanet (about Uranus' diameter, though over 50% its mass) known to transit its host star and is currently the nearest (33 ly). Its temperature (712K) was measured to be higher than what it would be purely from radiation (520K), perhaps due to a greenhouse effect, somewhat higher than Venus. It was originally thought to have a layer of "hot ice", water solidified due to high pressures. It turned out that it was larger than thought and hot ice was not needed. It could still be a rocky super-Earth. It was later found to have a remarkably low levels of Methane and high levels of Carbon Monoxide for its 800K temperature. Possible explanations include Methane being changed into hydrocarbon polymers due to its star's ultraviolet radiation, CO being drafted upwards with winds, or observational defects. Later, due to lack of detection of chemical signatures through the backlit atmosphere, it was concluded that high altitude clouds, perhaps made of potassium chloride or zink sulphide dust, were blocking the detection. This could be the first detection of clouds of a Neptunian. An alternate theory is that the atmosphere is filled with heavy compounds, such as water, carbond dioxide, which would compress the atmosphere and make it difficult to detect. After detection of a huge comet-like tail of Hydrogen trailing and wrapping around its orbit led to the most recent theory that it lost its Hydrogen to uv radiation and was left with a Helium dominated atmosphere with plenty of CO instead of CH4. It's significant eccentricity suggests a possible neighboring planet. Planet c was announced to be the smallest known exoplanet (1.5 Earth's diameter), but was later retracted because variations in transit timing of the first planet did not occur and the proposed orbit would be unstable. It is still thought that a second planet of some kind is possible in the system. Candidate UCF-1.01 was detected by a student in the UCF's astronomy department using the Spitzer Space Telescope. It is about 2/3 Earth's diameter (smaller than all but one confirmed exoplanet), orbits around its star in 1.5 days, and at 1000F may be a lava world without an atmosphere. UCF-1.02 also may exist. Both are thought to be about 1/3 as massive as the Earth, but are too small to get their mass measured and thus too small to be confirmed with present technology.

My Thoughts[]

Can we start calling these things Helium Giants? Are most Warm Neptunes going to be Helium Giants? Oh, only really old ones like this one. Do they still think cloud-cover is preventing chemical signatures from being read? But they read CO, doesn't that count?

Gliese 436 System Web Pages[]

Gliese 436 System Artwork[]

Gliese 436 System In the News[]

Neptunian Planet b Discovered (Sep 2004)[]

The second/third Neptunian is detected (along with 55 Cancri e, making Gliese 436 the second known red dwarf to harbor planets.

Controversy Over First Neptunian Discovered (Sep 2004)[]

Planet Made of "Hot Ice" (May 2007)[]

Planet b becomes the smallest exoplanet known to transit its host star and the nearest. It has been characterized by having a steamy atmosphere and "hot ice".

New Spitzer Radius Measurements (Jul 2007)[]

Spitzer Transit and Secondary Eclipse Photometry (Jul 2007)[]

Superearth Planet Suspected (Jan 2008)[]

New Hubble Transit Light Curve (Apr 2008)[]

Planet c Confirmed (Apr 2008)[]

Planet c Retracted (May 2008)[]

Low Levels of Methane and High Levels of Carbon Monoxide Detected (Apr 2010)[]

Still Puzzling over Low Methane Level (Sep 2010)[]

Alien Planets with No Spin May be Too Harsh for Life (Dec 2011)[]

Two New Candidate Planets Found by UCF Smaller Than Earth (Jul 2012)[]

Cloud Cover Announced for Planet b (Dec 2013)[]

See also GJ 1214 System

Hydrogen Tail Detected by Hubble (Apr 2014)[]

Hydrogen Tail Confirmed (Jun 2015)[]

Atmosphere Likely Helium (Jun 2015)[]

Gliese 436 System Fun Links[]

  • article - Is the planet Republican or Democrat?

See Also[]