HR 8799 e is a large

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

, orbiting the

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

HR 8799 HR 8799 is a roughly 30 million-year-old main-sequence star located away from Earth in the constellation of Pegasus. It has roughly 1.5 times the Sun's mass and 4.9 times its luminosity. It is part of a system that also c ...

, which lies 129

light-years A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

. This

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...

is between 5 and 10 times the

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

, the largest planet in the

Planetary System A planetary system is a set of gravitationally In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interacti ...

. Due to their young age and high

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

all four discovered planets in the HR 8799 system are large, compared to all gas giants in the Solar System.

Description

HR 8799 e is the fourth planet orbiting HR 8799 in order of discovery. It is a young, hot and massive

, and is fairly close to its star, lying just between the

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

and

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...

in the Solar System. The planet is still glowing

red Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...

-hot. HR 8799 e is the innermost known planet as it orbits closer to its star than the other three known planets in this

planetary system A planetary system is a set of gravitationally In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interacti ...

. This planet orbits at an estimated distance of 14.5 AU based on the relationship between

angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...

measured by direct imaging observations and the star's distance from Earth. The estimated period of this planet if the orbit is face-on is about 50

years A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the hou ...

Discovery

A team of researchers led by Christian Marois at the National Research Council's Herzberg Institute of Astrophysics identified the planet from data taken in 2009 and 2010 using the

W.M. Keck Observatory The W. M. Keck Observatory is an astronomical observatory with two telescopes at an elevation of 4,145 meters (13,600 ft) near the summit of Mauna Kea in the U.S. state of Hawaii. Both telescopes have aperture primary mirrors, and when comp ...

in the K and L spectral bands. They announced their findings on 22 November 2010. A separate work reporting the detection of HR 8799 e, led by Thayne Currie and using the

Very Large Telescope The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each with a primary mirror 8.2 m across, ...

, was made public six weeks later. Observations obtained since then with the

Large Binocular Telescope The Large Binocular Telescope (LBT) is an optical telescope for astronomy located on Mount Graham, in the Pinaleno Mountains of southeastern Arizona, United States. It is a part of the Mount Graham International Observatory. When using both 8 ...

show that HR 8799 e has a spectrum and temperature similar to HR 8799 c and d.

Observations

In 2013, near infrared spectroscopy from 995 to 1769 nanometers made with the Palomar Observatory showed evidence of

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Eart ...

and

acetylene Acetylene (systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...

but no signs of

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

or carbon dioxide gas. There is no explanation as to why the planet shows strong methane absorption, but the other 3 planets in this system do not, despite all 4 planets having similar atmospheric temperatures. On 27 March 2019, the

European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...

announced the result of their

astronomical interferometer An astronomical interferometer or telescope array is a set of separate telescopes, mirror segments, or radio telescope antenna (radio), antennas that work together as a single telescope to provide higher resolution images of astronomical objects ...

(VLTI) imaging of HR 8799 e employing the GRAVITY instrument. This was the first direct observation of any exoplanet using

optical interferometry Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opti ...

. A spectrum ten times more detailed than earlier observations revealed a complex exoplanetary atmosphere with clouds of iron and silicates swirling in a planet-wide storm. Team leader Sylvestre Lacour said:

"Our analysis showed that HR8799e has an atmosphere containing far more carbon monoxide than methane — something not expected from equilibrium chemistry. We can best explain this surprising result with high vertical winds within the atmosphere preventing the carbon monoxide from reacting with hydrogen to form methane."

The observations with GRAVITY confirmed the

spectral type In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

of ~L7 for the planet HR 8799 e. Previously the spectral type suggested a higher temperature than the measured

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

. The GRAVITY observations showed that the planet has a low

surface gravity The surface gravity, ''g'', of an astronomical object is the gravitational acceleration experienced at its surface at the equator, including the effects of rotation. The surface gravity may be thought of as the acceleration due to gravity experien ...

, which solved the discrepancy. A low surface gravity is also observed for many young

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

s and is seen as an indicator of youth. The detection of water and carbon monoxide in planetary atmosphere was announced in 2021.

References

External links

{{Sky, 23, 07, 28.7150, +, 21, 08, 03.302, 129 HR 8799 Exoplanets discovered in 2010 Pegasus (constellation) Giant planets Exoplanets detected by direct imaging Exoplanets detected by astrometry