James Webb, Hubble’s successor telescope, but technically very different

The new James Webb space telescope is called to be the successor to Hubble, but between the two, more than 30 years have passed and technologically they are very diverse. The size of your primary mirror and its ability to see infrared light make the main differences.

The James Webb, the result of a collaboration between the European Space Agency (ESA), NASA and the Canadian Space Agency will become the most powerful telescope launched into space on the 24th, a kind of “time machine” that will observe places in the universe up to now unreachable.

The differences between the James Webb (JW) and Hubble are many, from its shape and size, to the distance at which it will operate, 1.5 million kilometers from Earth, which makes it impossible to send manned missions to repair or upgrade it.

The researcher at the Center for Astrobiology (CAB, CSIC-INTA) Santiago Arribas and Anthony Marston, from ESA, summarize for Efe some of the characteristics of the new JW in front of Hubble, which with more than 30 years of service occupies a place in the collective imagination for its impressive photographs.

Primary mirror

JW’s primary mirror measures 6.5 meters, compared to Hubble’s 2.4 meters, more than seven times in area. The larger the mirror, the further in distance it can be accessed, which means further back in time, Arribas says.

Being larger also provides more resolving power, you can see – Marston emphasizes – more details, get closer to certain small sources of light or separate the light from objects that are close to each other.

The mirror acts as “a bucket that collects the rain, only in this case it collects light” and being older it is “A wider cube, so it can collect more light and see objects that are weaker in intensity or that are further away”.

The size of the mirror is so important, Arribas points out, because JW is going to study “extremely distant” objects, which “implies that they correspond to earlier moments in the history of the universe.”

So much so that it will be able to detect the first galaxies, stars and black holes. “We are talking about when the universe was on the order of 5% or less of the current age, which is about 13.7 billion years.”

Infrared vision

Another important difference is that JW will observe the universe in the infrared spectrum, while Hubble is primarily focused on visible light.

As the universe is expanding, there is a relative movement between distant objects that emit light and us that receive it, Arribas explains.

This movement causes the light they emit in the visible spectrum, when it travels towards us, to move in wavelength towards the infrared, hence the need for detectors that can identify it.

Infrared light also makes it possible to “penetrate deeper” into areas with a lot of gas and dust, such as regions where stars and planet systems form.

Infrared light – Marston adds – also comes from colder astronomical objects, such as planets, so capturing it facilitates “the observation of their signature around the stars.”

An untraditional way

At first glance, the most fundamental difference is the non-traditional shape of the JW, “which draws a lot of attention”, highlights Arribas. To begin with, it doesn’t have a tube, like Hubble, to protect its mirrors, “because it doesn’t need one.”

Opposite Hubble’s one-piece main mirror, JW’s is divided into 18 independent hexagonal-shaped segments.

The reason is that no rocket is wide enough to fit the telescope, Marston says, and it has to travel folded. The deployment of the JW, in several phases, will be one of the most delicate moments of its commissioning.

Arribas points out a curiosity: The JW mirrors are yellow because they are covered with a thin layer of gold, which is the material that best reflects the infrared.

The telescope also has a solar shield the size of a tennis court, made up of five layers of a special material to prevent – he explains – the Sun from hitting the telescope and its four instruments, heating them up.

This “kind of umbrella” manages to cool it to temperatures of -230 degrees, because if it were heated it would emit radiation in the infrared that “would be confused with what we want to measure.”

Distance from Earth

While Hubble “is here next door”, 570 kilometers orbiting the Earth, the JW will be located at a point called Lagrange 2, at 1.5 million and will orbit the Sun.

They are about five times the distance from the Earth to the Moon, which makes it impossible to send manned missions to solve problems or update it as it has been done with Hubble, highlights Arribas.

“To minimize the possibility of failures with catastrophic consequences” some of its critical components are redundant and between the four instruments there is “a certain degree of overlap in terms of the type of science they can do.”

JW will have a limited lifetime. Due to the location where it will operate, it will sometimes need propulsion to correct and maintain the orbit correctly and when the fuel runs out it will no longer be possible to do so. Arribas points out that the expected time is about ten years.