This is a copy of the published version, or version of record, available on the publisher's website. This version does not track changes, errata, or withdrawals on the publisher's site.

This is a copy of the published version, or version of record, available on the publisher's website. This version does not track changes, errata, or withdrawals on the publisher's site.

This is a copy of the published version, or version of record, available on the publisher's website. This version does not track changes, errata, or withdrawals on the publisher's site.

This is a copy of the published version, or version of record, available on the publisher's website. This version does not track changes, errata, or withdrawals on the publisher's site.

Ariel (Atmospheric Remote-Sensing Infrared Exoplanet Large Survey) is the adopted M4 mission of ESA "Cosmic Vision" program. Its purpose is to conduct a survey of the atmospheres of known exoplanets through transit spectroscopy. Launch is scheduled for 2029.Ariel scientific payload consists of an off-axis, unobscured Cassegrain telescope feeding a set of photometers and spectrometers in the waveband between 0.5 and 7.8 µm, and operating at cryogenic temperatures.The Ariel Telescope consists of a primary parabolic mirror (M1) with an elliptical aperture of 1.1 m of major axis and 0.7 m of minor axis, followed by a hyperbolic secondary (M2) , a parabolic recollimating tertiary (M3) and a flat folding mirror (M4).The Primary mirror is a very innovative device made of lightened aluminum. Aluminum mirrors for cryogenic instruments and for space application are already in use, but never before now it has been attempted the creation of such a large mirror made entirely of aluminum: this means that the production process must be completely revised and finetuned, finding new solutions, studying the thermal processes and paying a great care to the quality check.