Posted 18 August 2022 in Astronomy, Blog, Science, Space.

Much has been made of the near-perfect launch of the James Webb Space Telescope (JWST) 7 months ago and its successful deployment 1.5 million kilometres from Earth. However, the truly important part of the mission will be disseminating the data to scientists to enable them to explore the universe, as without that the mission is futile. Mark McCaughrean from the European Space Agency (ESA) and two of the team from the European Space Astronomy Centre (ESAC) Science Data Centre (ESDC) explain how this will happen.

This is an extract from OpenSpace 30 magazine. Find out more in the complete article on the James Webb Space Telescope by subscribing to OpenSpace.

On 25 December 2021, JWST was launched into space on board a European-built Ariane 5 rocket. After years of delays, the scientific community was rewarded by a perfectly aligned launch towards its final orbital position, where it will be shielded from the light and heat of the Sun, Earth and Moon.

James Webb Space Telescope liftoff on Ariane 5 copyright ESA CNES Arianespace
The James Webb Space Telescope was launched on board an Ariane 5 rocket on 25 December 2021. © ESA/CNES/Arianespace

Following the telescope’s month-long journey to its new home and the deployment of its optics and sunshield, engineers and scientists have been working hard to set up and test the instruments. Now the challenge is for the scientists to start their planned experiments using JWST’s four infrared cameras and spectrometers – something that involves a whole chain of people and processes, from inception to discovery.

Choosing experiments

There are three main ways that the scientific community can get to use JWST.

  • ‘General Observer’ proposals, submitted to roughly annual deadlines – the winning proposers get privileged access to analyze the data for up to 12 months, after which it will be made available in the public archive.
  • ‘Early Release Science’ research programmes to enable the science community to test out the various instrument capabilities and get to grips with the data they produce – the data will made available in the public domain immediately.
  • ‘Guaranteed Time Observations’ allocated almost 20 years ago to the teams selected to develop JWST’s scientific instruments and individuals who provided expert knowledge.

The selection of scientific observations for JWST is highly competitive. The winning proposals may request anything from a handful to hundreds of hours of observing time. Once time has been allocated, further complicated work is needed to prepare the detailed observing sequences and to schedule them.

Delivering the data

Data will be delivered from JWST to the Space Telescope Science Institute in Baltimore, USA, with up to 28.6 gigabytes of science data sent in a 4-hour period twice a day. This data is pre-processed to split it down into science, engineering and housekeeping data. The science data is then processed to different levels, firstly to remove instrumental signatures and then calibrated to yield measurements in physical units.

“Normalizing the response function of the detectors is a big deal in the infrared,” clarifies Mark McCaughrean, Senior Advisor for Science and Exploration at ESA. “They are not the same as optical CCDs – they have lots of quirks and therefore the data requires various calibration steps. This calibration pipeline is run by the Space Telescope Science Institute. Most scientists will use calibrated data from the pipeline, but some may want to tweak the process, because a one-size-fits-all calibration might not be accurate enough for their specific scientific needs.”

Image known as Webb's first deep field taken by the James Webb Space Telescope in 2022
Image known as ‘Webb’s first deep field’ taken by the James Webb Space Telescope in 2022. © NASA, ESA, CSA and STScI

It takes just 1 to 2 hours between an observation being made on one of the telescope’s instruments to the data being available in the archive(s).

The Mikulski Archive for Space Telescopes (MAST) in Baltimore is the main point of entry for scientists with privileged access to the data from their own projects. Once the data becomes public, it will also be stored at ESDC in Spain and the Canadian Astronomy Data Centre in Victoria, British Columbia. All the public data and metadata is automatically synchronized across the three archives, including all the different levels of calibrated data within the pipeline.

The public archive creates a valuable source of data for future scientific endeavours in addition to the original projects. “The long-term curation and quality of this archival data is incredibly important,” adds Mark McCaughrean.

The role of ESDC

The JWST data and metadata will be the same at all three archives, but the way it is made available is up to each organization. In addition, each archive hosts data from a different set of missions. At ESDC, for example, this includes all of ESA’s own space science missions and third-party missions ESA has been involved in. The total archive size before JWST data started being imported was over 700 terabytes, and it is estimated that JWST will add a petabyte of data over the first 10 years of the mission.

Maria Arevalo Sanchez and Javier Espinosa, both DevOps Software and Database Engineers, are two of the 23 RHEA engineers working on the archives at ESDC. Maria explains: “We provide access to the science data from ESA’s astronomy, planetary science and heliophysics missions and from Hubble and JWST.

“We build the means to store the data in the infrastructure we have at ESAC and also the ways to retrieve that data and make it available to the scientific community. This includes providing graphical user interfaces and other programmatic services to access the data. Scientists can build their own scripts to access the data, while the Web user interface allows anyone to discover and explore the data they are interested in.

“Our aim is to give added value to the data through the work we do on the user interface for a user-friendly exploration and retrieval of data products, and the ways we enable users to access the services at ESDC. For this we use the metadata, which describes what has been observed by which mission, on which date, by which instrument and so on.”

The ESASky interface
ESASky offers access to data and images from many space missions for scientists and the public. © ESA

ESDC offers access to separate archives for each mission. In addition, ESDC has built ESASky, described by Javier Espinosa as: “An interface for all astronomy missions where you can look at the sky and navigate in a similar way to using Google Maps, with observations from all the missions, also including some external missions”.

ESASky uses the more interesting science products from each mission’s archive and offers a ‘Science’ interface plus an ‘Explorer’ interface designed for the general public (including Hubble outreach images), with a range of filtering options.

Looking back in time

The cost and manpower involved in a mission as big as JWST have led the scientific community, those involved in JWST’s development and observers to have high expectations about the achievements and scientific progress that JWST will unleash.

Building the James Webb Space Telescope
Building the James Webb Space Telescope: the 18 hexagonal mirror segments together measure 6.5 metres from side to side and have an area of just over 25 square metres.

“I often call JWST a space-time machine,” says Mark McCaughrean. “It is not only looking out into space, but also back in time – one of the key goals of the mission is to find galaxies so faint and so distant that it has taken billions of years for their light to reach us. We will be probing back to within a 100 million years or so after the Big Bang, in search of ‘first light’ objects – the first stars and galaxies that ever formed.

“We will also be studying the evolution of stars and galaxies over cosmic time. We will be trying to understand how stars like the Sun formed and how our Solar System was born by looking at places where this is still going on today. We have built an amazing machine – almost a modern-day cathedral in terms of its complexity and the time it has taken – which will let us answer some of these questions.”

Find out more

Read the complete article in OpenSpace 30 magazine – out now.


Main image: © ESA/ATG medialab