Alpha Centauri Bb

File:ESO - The Radial Velocity Method (by).jpg

File:A fly-through of the Alpha Centauri system.ogv

Starting in February 2008, and continuing through July 2011, a team of European astronomers,{{cite web|url=http://www.eso.org/public/news/eso1241/ |title=Planet Found in Nearest Star System to Earth |publisher=European Southern Observatory |date=16 October 2012 |access-date=17 October 2012}} mainly from the Observatory of Geneva and from the Centre for Astrophysics of the University of Porto, recorded measurements of Alpha Centauri B's radial velocity with European Southern Observatory's HARPS echelle spectrograph at the La Silla Observatory in Chile.{{cite web|first=Seth |last=Borenstein |url=https://abcnews.go.com/Technology/wireStory/earth-sized-planet-found-solar-system-17492821#.UH3VzFHwF8E |title=Earth-Sized Planet Found Just Outside Solar System |work=ABC News |date=17 October 2012 |access-date=17 October 2012}} The team made 459 observations of Alpha Centauri B's color spectrum over a four-year period, then used statistical filters to remove known sources of variance.{{cite journal

| last = Dumusque | first = X.

| author2 = Pepe, F.

| author3 = Lovis, C.

| author4 = Ségransan, D.

| author5 = Sahlmann, J.

| author6 = Benz, W.

| author7 = Bouchy, F.

| author8 = Mayor, M. | authorlink8 = Michel Mayor

| author9 = Queloz, D. | authorlink9 = Didier Queloz

| author10 = Santos, N.

| author11 = Udry, S. | authorlink11 = Stéphane Udry

| display-authors = 8

| title = An Earth mass planet orbiting Alpha Centauri B (Supplementary Information)

| journal = Nature

| volume = 490 | issue = 7423| pages = 207–11| date = 17 October 2012

| url = http://www.nature.com/nature/journal/vaop/ncurrent/extref/nature11572-s1.pdf

| doi = 10.1038/nature11572 | access-date = 17 October 2012|bibcode = 2012Natur.491..207D | pmid=23075844| s2cid = 1110271

}}

On 16 October 2012, the team announced they had detected an Earth-mass planet in orbit around Alpha Centauri B. The discovery was presented in the scientific journal Nature, with lead author Xavier Dumusque, a graduate student at the University of Porto.{{cite web |url=http://www.astro.up.pt/caup/index.php?WID=114&CID=1&ID=82&Lang=uk |title=Xavier Dumusque C.V. |publisher=Centro de Astrofisica da Universidade do Porto |access-date=18 October 2012 |archive-url=https://web.archive.org/web/20110616091129/http://www.astro.up.pt/caup/index.php?WID=114&CID=1&ID=82&Lang=uk |archive-date=16 June 2011 |url-status=live }} He called their findings "a major step towards the detection of a twin Earth in the immediate vicinity of the Sun".

The team used the Doppler spectroscopy method to search for a planet.{{cite web|first=Phil|last=Plait|work=Discover|url=http://blogs.discovermagazine.com/badastronomy/2012/10/16/alpha-centauri-has-a-planet/|title=Alpha Centauri Has a Planet!|date=16 October 2012|access-date=18 October 2012}} As the body orbits the host star, its gravity would cause extremely small (semi-amplitude of about 0.5 m/s) periodic shifts in the host star's velocity. Variations of the line-of-sight velocity component cause tiny shifts in the star's spectrum. Using an extremely sensitive spectrometer, the team was able to infer variations of 0.51 m/s in Alpha Centauri B's radial velocity. European Southern Observatory called the findings the most precise measurements ever recorded using the technique. The team estimated the probability of a spurious detection at 0.02%.

Dumusque used a variety of mathematical transformations to isolate the planet's gravitational signal and remove the surrounding stellar noise. The transformations filtered out other sources of radial-velocity variance, including effects of starspots, photospheric granulation and rotation, as well as interference from the neighboring star Alpha Centauri A.{{cite web

| url=http://www.sciencenews.org/view/generic/id/345756/title/The_alien_next_door

| title = The alien next door: Newly discovered planet is just 4.4 light-years distant

| last = Drake

| first = Nadia

| author-link = Nadia Drake

| publisher = Science News

| date = 3 November 2012

| access-date = 21 October 2012

}} The final, derived radial-velocity measurements showed the periodic influence of the planet on the star, but were near the threshold of the HARPS instrument's sensory capabilities.{{cite web|title=ESPRESSO – Searching for other Worlds|url=http://espresso.astro.up.pt|access-date=18 October 2012|publisher=University of Porto|archive-url=https://web.archive.org/web/20101017053751/http://espresso.astro.up.pt/|archive-date=17 October 2010|url-status=dead}} (The long-term precision of HARPS is about 0.8 m/s.)

In a commentary piece that ran in Nature alongside the original paper, American exoplanet hunter Artie Hatzes praised the team's technical achievements and admitted he observed a planetlike signal amongst the data, but called it "a weak signal in the presence of a larger, more complicated signal". He stressed the need for further empirical confirmation, and opined that the existence of the planet was "still open to debate". (Hatzes had previously expressed scepticism about unproven methods of data analysis during the dispute over the unconfirmed planet Gliese 581g.){{cite web

| last=Overbye

| first = Dennis

| url = https://www.nytimes.com/2012/08/21/science/space/just-right-or-nonexistent-dispute-over-goldilocks-planet-gliese-581g.html

| title = A Planet 'Just Right' for Life? Perhaps, if It Exists

| work = New York Times

| date = 20 August 2012

| access-date = 18 October 2012}}

In October 2015, three years after the announcement of the initial finding, researchers from the University of Oxford published a paper entitled "Ghost in the Time Series", demonstrating flaws in the original analysis. Using the same data as Dumusque, the Oxford team found the signal was caused not by a planet, but instead was a mathematical artifact of the window function used to create the time series for the original observations. To prove this assertion, they replaced the actual astronomical data with randomly-generated noise, and obtained identical results. The team concluded that their analysis "underscores the difficulty of detecting weak planetary signals in RV data".

Dumusque agreed with this analysis, and conceded that the planet he had identified probably did not exist.

• Proxima Centauri b (Alpha Centauri Cb)
• Proxima Centauri c
• Alpha Centauri Bc
• Alpha Centauri in fiction
• Project Longshot

{{Reflist|30em}}

{{Alpha Centauri}}

{{nearest systems|1}}

{{exoplanet}}

{{2012 in space}}

Category:Alpha Centauri

Category:Centaurus

Category:Astronomical controversies

Category:Articles containing video clips

Category:Disproven exoplanets