Detecting the dip – using photometry to discover transiting exoplanets An important aspect of this technique is that it allows scientists to measure the mass of the planet, unlike the radial velocity technique that only provides a lower limit to the mass. The astrometric technique can be used to detect planets with periods ranging from several days to several years. In addition, due to their low surface temperatures, M-type dwarfs host potentially habitable planets at much closer distances than hotter and more massive stars. M-type dwarf stars are especially interesting for exoplanet searches because there are many and they have low mass – the latter meaning that they are subject to larger wobbles than their more massive counterparts orbited by a planet of a given mass. These red stars are cooler, smaller and less massive than the Sun (with masses ranging between 0.075 and 0.50 solar masses) and represent the most abundant stellar population in our Galaxy. Click here for video detailsīased on current estimates of the distribution of planets and their orbits, roughly 1000–1500 of these discoveries are expected to be planets orbiting M-type dwarf stars within a distance of 100 parsec (about 320 light-years) from us. With an anticipated astrometric precision around 10 microarcseconds for the brightest stars, scientists forecast that it will be possible to detect some tens of thousands of exoplanets out to 500 parsec (around 1600 light-years) from the Sun by measuring the wobble they cause in the path followed by their parent stars on the sky. So far, less than a handful of exoplanets have been discovered using this astrometric technique with ground-based observations, while astrometric information provided by ESA's Hipparcos mission (the predecessor of Gaia), the NASA/ESA Hubble Space Telescope, and large ground-based telescopes have been used to refine the orbit determination of planetary systems that had been discovered with the radial velocity method. The presence of one or more objects (other stars or planets) orbiting a star perturbs its motion, and this perturbation is reflected in the positions, which do not quite match a pure stellar motion described with parallax and proper motion.
Star and planet orbiting their common centre of mass.
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