A newly released image of the planet Neptune shows just how far telescope technology has come in recent years. This view of Neptune is almost impossibly clear compared with past attempts, thanks to a recent upgrade to the Very Large Telescope (VLT) at the European Southern Observatory (ESO) in Chile. You can actually make out cloud patterns on Neptune with the upgraded VLT, which is something even Hubble can’t do.
You’re probably thinking this image doesn’t look all that clear. Indeed, there are crisper snapshots of the outermost planet, but those came from NASA’s Voyager 2 during its 1989 flyby. There are no spacecraft in orbit of Neptune, so the only way to get new images of the gas giant is to capture them from 2.9 billion miles away on Earth.
Until now, Hubble was the best way to look at Neptune, but the planet is rather small and dim compared with most of the objects Hubble surveys. The comparison image below shows how much better the new VLT is for observing objects like Neptune compared with Hubble.
The Very Large Telescope consists of four separate 8.2 meter (27 foot) mirrors. That’s a lot of surface area to scan the sky, but Earth’s atmosphere distorts celestial objects. That’s why space telescopes like Hubble and the upcoming James Webb are so important. The ESO developed a new adaptive optics mode based on laser tomography to counteract that. The system consists of MUSE (Multi Unit Spectroscopic Explorer) and an optical unit called GALACSI.
Using adaptive optics with the VLT is like giving it eyeglasses that correct for atmospheric distortion. In order to correct the blur, you need to know how much the atmosphere is distorting light. The VLT projects four high-intensity lasers into space, which act like an artificial star. The blur detected from the laser tells the system how to change the mirror’s shape to take sharper images. As you can see below, Neptune is just a blurry disk without adaptive optics.
The newly released images were taken in “narrow-field mode.” That means the telescope can only observe a small part of the sky (like imaging Neptune). In wide-field mode, the VLT can take capture more of the sky, but the system can only correct for a kilometer of atmospheric distortion.
The upgraded VLT won’t be able to match the Webb Space Telescope, but it’s already operational, and NASA’s launch schedule for Webb keeps slipping.